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Color Logo / Cat. No. 26-2722 / Year: 1982 - TRS

1. 28 116 Logical 116 O ant 10 115 Mailbox ea 91 adn 91 117 MATE 250 45 ce Sm Eds 93 117 MAKE ER ee D 64 113 Master turtle 4 e hen Dee hA 71 ME setas a f n ARO 16 117 Message ito ve heehee ERE S 91 Modest 6 107 Pere prs 39 Multiple 71 Multiprogramming 71 5 eR eR 17 NEAR NG RER ais wea 74 117 NOWRAP a ea aa eed 43 113 OK Set ca deed ute EE TR 57 Overlay x ee a eR 53 PADDLE sa au 94 117 PG ats er tale 31 115 nee 35 115 31 115 PENDOWN 35 115 PENUPB essersi or 35 115 Photograph dee 4 wig esee 41 PRINT ari a 93 101 113 Printing 39 85 115 93 RANDOM 78 117 Recursion 2 22 2 2 2 224 48 Relational 116 REPEAT lue rd 21 99 112 Reset aan anne 6 RIGHE anche ara 8 115 ROM sun ren 5 39 BUDE ese ee 8 115 RUN mode 13 107 126 DAVE hotest ihn 39 SCAT zoom Pa O Bea ME Sete 16 Screen dimension 110 Screen position 110 nite ed a 16 S
2. TO CHASER X WHILE 1 HOME PU WHILE NEAR 2 gt 12 MAKE X MAIL 1 IF X IF X 1 FD 16 ELSE RT X SEND 1 END CHASER includes nested WHILE statements The first one starts the chaser and runs forever The inner one runs until a capture is made The definition of a capture is that the value returned by the NEAR function is 12 or less The portion of the procedure controlled by the condition NEAR 2 gt 12 is identical to that in RUNNER Remember that the NEAR function returns the total number of X and Y steps from the current turtle to the designated turtle here to turtle 2 Thus the inner part of the procedure says to continue checking mail and making moves as long as the runner is more than 12 steps away If the runner is not more than 12 steps away then turtle 3 the chaser sends a message 1 to the scorekeeper turtle 0 Having sent the message the chaser returns to the home position and the chase begins again 92 Now we turn to the procedure for the scorekeeper TO SCOREKEEPER S HT SX 200 SY 180 WHILE 1 PRINT PRINT S WHILE MAIL 255 0 MAKE S S 1 END Again there are several new ideas in this procedure The first steps are to hide the turtle and to position it to keep the scoreboard We set the initial score to 0 by the call of the procedure and again use a WHILE 1 The PRINT statement causes anything contained in quotes to be printed on the screen at the current turtle position T
3. 1 PD FD 1 FD1 BK 1 PU LT 90 END The following program again makes use of the SX and SY here to get the right relative spacing of independent parts The correct numbers for the two are found by trial and error Try the procedures with a variety of pen colors and backgrounds 36 TO KIRSTIN CLEAR 5 60 SY 80 REPEAT 18 PENT 20 RT 20 SX 95 SY 82 REPEAT 9 PENT 15 RT 40 END TO PENT SIDE REPEAT 5 FD SIDE LT 72 FD SIDE END 37 9 SAVING LOADING AND PRINTING YOUR COLOR LOGO PROCEDURES Although Color LOGO procedures can do an amazing amount with very little code we still don t want to have to retype procedures every time we start up Procedures can be stored on cassette tape or on disk just cassette on ROM version For simplicity all procedures in memory are stored as one module and all procedures in a module on disk or tape are loaded No directories are kept for the modules a directory entry could be almost as long as many of the procedures in Color LOGO To move procedures to and from cassette or diskette we must be in BREAK mode By now you probably have a number of procedures in memory that you would like to keep Get into EDIT mode and delete any you do not want to save To delete a procedure you must delete it character by character Then get into BREAK mode BREAK key and press S At this point the prompt will be LOGO SAVE You now have to tell the computer where to save the proced
4. NOWRAP WRAP HATCH expr procname arglist SEND expr expr This is the last statement in a procedure Execution of an END is equivalent to that of the STOP statement VANISH takes the current turtle out of existence The value of the expression is assigned to the variable The literal text or the expression value is displayed at the turtle location The turtle is not moved Normally the screen is in wrap mode That is a turtle which runs off the screen will come back on the opposite edge Execution of the NOWRAP statement takes the screen out of wrap mode If a turtle then runs off the screen the program will terminate with an OUT OF BOUNDS error message Puts the screen back in wrap mode Creates a new turtle The turtle will start at the same X Y position as its parent the turtle that HATCHed it and will be pointed in the same direction It will have the standard turtle shape The expression value becomes the new turtle s identification number a number from 1 to 254 The procname specifies the procedure to be exe cuted by the new turtle The arglist is optional it specifies the arguments to be passed to the procedure The new turtle runs simultaneously with the other active turtles A message is sent to the specified turtle The first ex pression value denotes the identification of the turtle to which the message is sent A value of 255 denotes that the message is being sent to the first t
5. LENGTH TIMES the command DESIGN 40 24 causes the value 40 to be assigned to LENGTH and the value 24 to be assigned to TIMES Notice also that the name of the variable in the call of SQUARE SQUARE LENGTH need not be the same as the name in the definition of SQUARE TO SQUARE SIDE At the time SQUARE is called LENGTH has a value for example 4 which is assigned by SQUARE to the variable SIDE Variables listed on the TO statement are local to the procedure Again we illustrate using the previous programs Enter TO DESIGN LENGTH N REPEAT N SQUARE LENGTH RT 369 N END TO SQUARE N REPEAT 4 FD N RT 99 END Here the variable name N is used for two different quantities one in the main procedure DESIGN and another in the subprocedure SQUARE This causes no problems or confusion because the variables for the two procedures are kept completely separate in the memory The variable N in the main procedure is not the same memory location as the variable N in the subprocedure If we want a variable to be local to a procedure we mention it in the TO statement which begins the procedure The maximum number of local variables for a procedure is five We also can create global variables variables which use a common memory location in all procedures in which they appear Global variables are created by using them in a procedure without including them in the TO statement This provides a convenient way to share information among pro
6. one command in the procedure will be executed For example when you start step a the first executes IF N lt 18 the second executes FD N which you can see the third ENTER executes RT 45 again visible and the fourth ENTER executes the recursive call You can follow the table exactly as long as you realize that the statement IF N lt 18 STOP is one statement if the condition is false but two statements if the condition is true execute the STOP A step iri the table is counted as all the lines executed from when a level is entered until the level is exited A level can be exited in three ways by a STOP or an END which completes the procedure at that level and goes up or by a call of another procedure which leaves the current procedure incomplete and goes down Instead of giving an elaborate account in words of what is happening we recommend that you run the program in single step mode and follow the table and the program in parallel If you get confused start over and try again Recursion is a little complex but it is so powerful that it is worth the effort to understand 48 The next program draws a figure which is called a fractal A fractal is a figure which looks the same no matter what magnification is used to view it of course we are limited by the screen resolution here In this example we ll start with the basic shape ee The idea is that each of these four lines should be made up of tha
7. soit is addressed to turtle 0 That s more like it If you want to see in a bit more detail what is actually happening you might want to slow down the speed You can slow any procedure by inserting a SLOW command TO TEST SLOW 30 HATCH 1 BOX 50 30 60 HATCH 2 BOX 40 180 40 HATCH 3 BOX 60 100 20 BOX 20 150 120 END 72 The number after SLOW tells the computer how much to slow down The number must be between and 127 Zero is full speed and 127 is the slowest speed The SLOW command sets a speed for all procedures which will remain unchanged until reset with another SLOW command or until RUN mode is exited and then reentered Before we leave this example notice that at the completion of each turtle s procedure the turtle disappears so that at the end only turtle remains Of course we can use many procedures for the various turtles Try TO TEST2 HATCH 1 BOX 50 30 60 HATCH 2 BOX 49 180 90 HATCH 3 BOX 60 100 20 HATCH 4 CIRCLE 3 30 140 HATCH 5 CIRCLE 4 180 120 CIRCLE 5 90 90 END This procedure can be used to point out one potentially troublesome point What if we altered the procedure by making the procedure for turtle 0 BOX say BOX 80 90 90 If you try this you will find that the circles are not completed and the two turtles drawing the circles remain on the screen This is because turtle 0 runs out of commands before the others are finished To avoid the problem always put the procedure for turtle 0 last and assign turtle 0
8. t going to use it in this example there is a way to send a general message to the first turtle that picks up its mail We just use the turtle address 255 then the next turtle that inquires will get the message If we wanted to send an all points bulletin to all turtles we could do so by setting a global variable see Chapter 6 The rest of GETKEYS is just more of the same We check for each of the keys which control the runner and send a message to turtle 2 if one of them is depressed and we do the same for the three keys which control turtle 3 Notice that the WHILE 1 causes turtle 1 to continue to poll the keyboard forever There are certain features of Color LOGO which make this part of the programming very simple By assigning one turtle the task of watching the keyboard at all times we make sure that the two players have equal access to control we are very unlikely to lose keystrokes while something else is happening and provision for regular polling of the keyboard is handled automatically by the logic which handles multiple turtles Now let s turn our attention to RUNNER TO RUNNER X PU SX X SHAPE FFFFFFFFUBBBRRFD FFUBBBDBBB WHILE 1 MAKE X MAIL 1 IF X IF X 1 FD 8 ELSE RT X END RUNNER sets a starting position for the runner lifts the pen so that the runner leaves no tracks which makes no difference in the chase but keeps the screen clean and draws a shape so that the runner will look different We then
9. very heavily on speed Things happen which force the player to react faster and faster until finally they fail You ve already gotten some feel for the speed at which animation runs in Color LOGO it s not going to be fast enough to create shoot em up space games that will hold interest for long However it does have capabilities such that the user can create rather than just play such games If you want to create games which will also be challenging to play using Color LOGO then you might try to think of games where coordination of several moving objects is the challenge thus lower speed is no limitation or games where there is sufficient strategy that the player must think while playing Our first sample game is called CATCHEM There are two players or one two handed player who manipulate objects on the screen by pressing keys on the keyboard The object is for the chaser to catch the runner When the chaser catches the runner the scorekeeper changes the score and a new chase starts There is an advantage to using multiple turtles here as we can assign each turtle one task This simplifies the programming greatly for example we do not have to move a cursor to the scoreboard to change the score and then return to make the next move The master procedure simply names the procedures and assigns the four tasks to four turtles We use turtle and three others TO CATCHEM CLEAR HATCH 1 GETKEYS HATCH 2 RUNNER 20 HATCH 3 CHASER SCOREKEE
10. 128 Y 96 The turtle heading at HOME is zero degrees or straight up The screen dimension in the X direction across the screen goes from 0 at the left edge to 255 at the right edge The screen dimension in the Y direction up and down goes from 0 at the left edge to 255 at the right edge The screen dimension in the Y direction up and down goes from at the bottom to 191 at the top The lower left hand corner of the screen has coordinates 0 0 The upper right corner has coordinates 255 191 The screen is normally a wrap around space that is if the turtle runs off the top of the screen it appears on the bottom If it runs off the left it appears on the right etc In that sense the plane on which the turtle walks is infinite in any direction The turtle may be pointed in any direction from 0 to 359 degrees Straight up is 0 degrees and the direction increases as the turtle rotates to the right or in a clockwise direction RUN MODE RUN MODE is entered from the BREAK MODE by entering R When RUN MODE is entered the screen is cleared and the turtle appears at the bottom position A TEXT WINDOW of three lines exists at the bottom of the screen The user enters turtle graphics commands or calls Color LOGO procedures that have been entered earlier via the EDIT or DOODLE MODE The user can enter any of the following commands directly in RUN MODE However in RUN MODE no more than one command may be entered on a line Once the ENTER key is
11. 15 Try each of the keys in turn Of course 1 CLEAR will clear the screen so you won t have much time to see that one Note the correspondence between the symbols on the keys the symbols on the bottom of the screen and the action of the turtle Remember that a turn of 15 degrees is not enough to turn the turtle shape but three 15 degree turns in a row is enough to produce a visible turn OK now that you have a bit of the idea of DOODLE mode let s try to make something useful To get a fresh start exit DOODLE mode by pressing BREAK This puts you in BREAK mode Clear the procedure space by pressing SHIFT CLEAR Get into the RUN mode press R and then get into the DOODLE mode press The reason that we always get into the DOODLE mode from RUN mode is that we may want to draw patterns on the screen in RUN mode for the child to interact with or copy in DOODLE mode Notice that the screen is not cleared when we enter DOODLE mode Now let s name the procedure we are creating S by typing an S and pressing ENTER 58 Begin by drawing a box using the top row of keys When the box is completed exit DOODLE mode by pressing the BREAK key Then get into the RUN mode and run the procedure S The only difference between this and the procedure we earlier called BOX is that S is a little slower To see that S actually exists as a procedure get into EDIT mode and look at procedure S Notice that itis there with ex
12. 2 45 16K users won t see all of this picture Incidentally if you want to get rid of the type at the bottom of the screen you can use a procedure like the following TO TEST SIZE ANGLE STEP CLEAR INSPI SIZE ANGLE STEP END The analysis of INSPI is so similar to that of POLYSPI that we won t bother to give it We now turn to the more complex type of recursion recursion where returns to the higher levels are actually made Another popular program in turtle geometry is called TREE TO TREE N IF N lt 2 STOP FD N RT 15 TREE 3 N 4 LT 30 TREE 3 N 4 RT 15 BK N END oOAN OA PWN 46 The line numbers are not part of the procedure they are there for reference in our discussion of the procedure Enter this procedure without the line numbers of course and try running it with a value of 20 to 30 for N You might try making the numerical factors in the two calls of TREE lines 4 and 6 of the procedure somewhat different thus producing an asymmetrical tree You also could try changing the angles but notice that the sum of the two right turns is equal to the left turn Now let s try to understand the program We have introduced two new ideas in line 1 The first is the conditional IF The IF must be followed by an expression which has a truth value In TREE the expression is N lt 2 If the current value of N is less than 2 then this expression is true and the rest of the statement wil
13. 30 RT 90 FD 50 RT 90 PC 1 FD 30 END TO FOUR REPEAT 4 BOX END TO MANY N REPEAT 2 N 3 FOUR RT 9 N END 32 Try it with N 90 If it is too slow or if you feel sorry for any turtle that has to run around at that speed for so long hide the turtle HT before calling MANY You might prefer the colors you get with a dark background Try setting the background to 0 and rerun the preceding two examples MANY 10 and MANY 99 33 8 OTHER TURTLE COMMANDS There are a few additional turtle commands which we have not yet used We can raise and lower the turtle s tail so we have the choice of leaving a track or not leaving a track The commands are just what you d guess PENUP abbreviated PU and PENDOWN abbreviated PD Let s illustrate by removing the lines of one color from the previous figure Change BOX to TO BOX PU FD 50 RT 90 PD PC2 FD 30 RT 90 FD 50 RT 90 PU FD 30 END and again run MANY 99 Every figure thus far has started in the center of the screen at a position called home When we get into the RUN mode the turtle automatically moves to home If we want to start the turtle somewhere else we can The turtle can be moved to an arbitrary and absolute screen position by means of the SETX abbreviated SX and the SETY abbreviated SY commands The results of these two commands are absolute not relative to the current position of the turtle No line is drawn and no change in heading is ma
14. Color LOGO it should not be written upon under BASIC Each Color LOGO module occupies 2 tracks or 36 sectors on the diskette 121 APPENDIX 2 MAKING A BACKUP COPY OF THE COLOR LOGO DISKETTE It is a good idea to make a copy of the Color LOGO diskette for everyday use The original Color LOGO diskette can be stored in a safe place to protect it from damage To make a backup copy follow the steps below One Drive TRS 80 Color Computer Disk System 1 10 Make sure that the Color Computer is properly connected to the color television or color video Plug the Color Computer Disk Controller into the slot on the right side of the computer Turn the color video and the Color Computer system on The computer s power switch is on the back left corner of the computer The disk drive switch is on the back of the drive in the upper corner When you see the prompt insert a new blank diskette into the disk drive Then type DI SI KILLJ NI I G and press ENTER When the prompt reappears remove the new diskette from the disk drive Place an adhesive tab provided with new diskettes over the square notch in the Color LOGO diskette If you do not have any tabs use a small piece of opaque tape Insert the Color LOGO diskette with the square notch up and the label facing right into the disk drive Close the disk drive latch B AJ C K UJ P _1 0 and press ENTER When you se
15. If more than one message is available for delivery then the oldest undelivered message is the one returned If no messages are available then a value of zero is returned 117 PADDLE arg returns a value from 0 to 63 denoting the position of one of the game paddles joysticks The arg is a value from 0 to 8 PADDLE 0 gives the UP DOWN of the left paddle PADDLE 1 gives the RIGHT LEFT of the left paddle PADDLE 2 gives the UP DOWN of the right paddle And PADDLE 3 gives the RIGHT LEFT of the right paddle For UP DOWN the minimum value is UP For RIGHT LEFT the minimum value is LEFT The arg designation shown above denotes an argument value passed to a procedure or func tion The argument can be a variable a number a function reference or an expression If the argument is an expression it must be enclosed in parentheses TURTLE SHAPE LIST The SHAPE statement is used to assign a new shape to the current turtle The shape of a turtle is made up of a pattern of dots on a grid The shape list tells Color LOGO how to draw the turtle pattern The turtle shape is automatically rotated to face in the direction the turtle is headed Drawing the turtle shape is similar to using normal turtle graphics commands to draw any shape The difference is that the commands which make up the shape list are a restricted and simplified form of the normal turtle graphics commands The commands allow a step of one pixel one square on a piece of graph paper
16. Mathematics Their Way by Mary Baratta Lorton Addison Wesley Publishing Company 1976 makes use of this technique for beginning mathematics and is a rich source of ideas for DOODLE mode projects Basically the approach is to write a procedure in the conventional way which will draw a figure or shape This can be placed on the screen in RUN mode The child is then asked to copy complete fill in invert rotate or in some way proceed with reference to the figure on the screen If the procedure the child develops while doing this is likely to be worth keeping for future use then the child should be working in DOODLE mode If it is not worth keeping or if it requires the more complex shapes then the child should be working with the OK Set of procedures Let s turn now to some specific activities A large number of exercises could be built around the idea of pattern continuation and generalization These activities are best suited to the OK Set so the following procedures should be added to that set One of the simplest types is a pattern which can be imposed on a line of dots First we draw two parallel lines of dots 61 TO DOTS CLEAR HT RT 90 SX5 SY 150 LINE OF DOTS SX5 SY 50 LINE OF DOTS END TO LINE OF DOTS REPEAT 20 DOT FD 12 END TO DOT FD1 PD RT 90 FD 1 REPEAT 4 RT 90 FD 2 PU BK1 LT90 BK 1 PU END DOT is a bit more elaborate than we need right now but later on we ll want to be sure that the dot is centered on the st
17. PC COLOR FD LENGTH LT 30 FD LENGTH RT 30 FD LENGTH END 102 Try this with SPIDER 45 Next we give one which will remind you of the start of every science fiction film you ve ever seen There is no picture in the manual for this one as the effect is all in the motion TO SPACETRAVEL COLORSET 1 BG 0 HT MAKE X 4 WHILE 1 HATCH 1 5 1 RT 67 HATCH 1 STAR2 RT 207 HATCH 1 STAR1 RT 114 HATCH 1 STAR2 RT 87 SETX XLOC ME 4 X IF NEAR 255 gt 30 MAKE X X 1 HATCH 1 PLANET VANISH END TO 5 1 HT SHAPE FFRRFRRF PU FD2 ST REPEAT 25 FD 3 END 103 TO STAR2 HT SHAPE F PU FD2 ST REPEAT 35 FD 3 END TO PLANET HT IF XLOC ME gt 128 SETH 75 ELSE SETH 300 FD 10 SHAPE FFRFFRFFRFFRFFR FFRFFRFF PU FD6 ST REPEAT 29 FD 4 END Here s one which shows the orbit of a moon around a planet and which makes use of multiple turtles to simplify the mathematics TO ORBIT COLORSET 1 BG FD 10 RT 90 REPEAT 8 FD 6 RT 45 FD 6 HOME PU SETH 90 SY 164 MAKE MOONPOS 0 SHAPE U FFFFFRRDFFRFFFFRFFFFRFFFF RFFFFRFFFFRFFFFR FFFFRF WHILE 1 REPEAT 4 HATCH 1 MOON MOONPOS REPEAT 6 MAKE MOONPOS MOONPOS 20 FD 10 RT 9 END TO MOON POS HT PU RT MOONPOS FD 20 SHAPE UFFFFRRDFRFFRFFRFFR FFRFFRFFRFFRF ST REPEAT 9 VANISH END 104 As our last example we give a final pretty pattern TO SAMPLE COLORSET 1 BG 0 NPOLY 8 12 3 SX 70 SY 72 N2POLY 8
18. RADIO SHACK D Except as provided herein RADIO SHACK MAKES NO WARRANTIES MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE E Some states do not allow limitations on how long an implied warranty lasts so the above limitation s may not apply to CUSTOMER IH LIMITATION OF LIABILITY A EXCEPT AS PROVIDED HEREIN RADIO SHACK SHALL HAVE NO LIABILITY OR RESPONSIBILITY TO CUSTOMER OR ANY OTHER PERSON OR ENTITY WITH RESPECT TO ANY LIABILITY LOSS OR DAMAGE CAUSED OR ALLEGED TO BE CAUSED DIRECTLY OR INDIRECTLY BY EQUIPMENT OR SOFTWARE SOLD LEASED LICENSED OR FURNISHED BY RADIO SHACK INCLUDING BUT NOT LIMITED TO ANY INTERRUPTION OF SERVICE LOSS OF BUSINESS OR ANTICIPATORY PROFITS OR CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR OPERATION OF THE EQUIPMENT OR SOFTWARE IN NO EVENT SHALL RADIO SHACK BE LIABLE FOR LOSS OF PROFITS OR ANY INDIRECT SPECIAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF ANY BREACH OF THIS WARRANTY OR IN ANY MANNER ARISING OUT OF OR CONNECTED WITH THE SALE LEASE LICENSE USE OR ANTICIPATED USE OF THE EQUIPMENT OR SOFTWARE NOTWITHSTANDING THE ABOVE LIMITATIONS AND WARRANTIES RADIO SHACK S LIABILITY HEREUNDER FOR DAMAGES INCURRED BY CUSTOMER OR OTHERS SHALL NOT EXCEED THE AMOUNT PAID BY CUSTOMER FOR THE PARTICULAR EQUIPMENT OR SOFTWARE INVOLVED 26 RADIO SHACK shall not be liable for any damages caused by delay in delivering or furnishing Equipment and or oftware C No ac
19. VANISH END 96 The SCOREKEEP procedure is essentially the same as before TO SCOREKEEP SCORE HT SX 200 SY 180 WHILE 1 PRINT PRINT SCORE WHILE MAIL 5 0 MAKE SCORE SCORE 1 COLORSET 1 COLORSET 0 END These two examples should help you to implement your own ideas for more complex games 97 17 GRAB BAG In this last chapter we give a final set of sample programs which we hope will give you ideas for your own projects We have introduced all the features of Color LOGO earlier so we will give these without lengthy comments The first set is controlled by the procedure BOND TO BOND WHILE 1 COLORSET 1 CLEAR HT DELAY 1000 TUNNEL WALK PAINT END TO WALK SX 28 MAN2 ST DELAY 2000 REPEAT 29 MAN2 DELAY 100 HT SX XLOC ME 3 MAN1 ST DELAY 100 MAN2 DELAY 800 SX XLOC ME DELAY 500 SX XLOC ME DELAY 500 SX XLOC ME DELAY 500 SX XLOC ME REPEAT 3 HT DELAY 20 ST DELAY 30 END TO TUNNEL PC 1 HT SX 60 SH REPEAT 18 FD 20 RT 124 FD 56 BK 56 LT 104 END TO 1 SHAPE RRUFFFLLDFLFR FFLFFRRRFLLFFRRF LFLLLFFRRFLFRRFL FFLFLFLFLFFLFRFF FFLLFRRRFLFFRFL FFRRFF END 16 16 99 100 TO MAN2 SHAPE RRUFFFLLDFF FFLFFRRRFLLFFRRF LFLLLFFRRFLFRRFL FFLFLFLFLFFLFRFF FFLLFRRRFLFFFFFF END TO PAINT PC2 HT MAKE X 1 REPEAT 3 COLORSET 0 DELAY 100 COLORSET 1 DELAY 100 SX 114 SY 102 SH 0 REPEAT 13 RAGGED X SX XLOC ME 6 SY YLOC ME 2 MAKE
20. X X 5 END TO RAGGED X REPEAT 8 FD X RT 135 FD8 BK 8 LT 90 END TO DELAY TIME REPEAT TIME END The next set is for a younger audience TO CLOCK DELAY INT CLEAR CLOCKFACE TIME DELAY INT END TO CLOCKFACE MAKE NUMBER 12 SY 180 SX 104 SH 90 REPEAT 12 FD 22 RT90 FD5 BK5 PU BK 10 PRINT NUMBER FD 10 PD 1790 FD 22 RT 30 MAKE NUMBER NUMBER 1 IF NUMBER gt 12 MAKE NUMBER 1 END TO TIME DELAY INTERVAL HT REPEAT 24 MAKE HR 0 WHILE HR 12 MAKE MIN 0 WHILE MIN lt 60 DIGITAL HR MIN PC 1 LITTLEHAND HR MIN PC2 BIGHAND MIN REPEAT DELAY PC3 LITTLEHAND HR MIN BIGHAND MIN MAKE MIN MIN INTERVAL MAKE HR HR 1 END TO BIGHAND MINUTE SX 128 SY 96 SH 6 MINUTE LT8 FD 60 RT30 FD 18 RT 130 FD 18 RT 32 FD 60 END 101 TO LITTLEHAND HOUR MINUTE SX 128 SY 96 SH 30 HOUR MINUTE 2 LT 32 FD 30 RT 60 FD 30 RT 120 FD 30 RT 60 FD 30 END TO DIGITAL HOUR MINUTES SX 0 SY 180 PRINT d SX 8 HOUR lt 9 amp HOUR 0 IF HOUR PRINT HOUR ELSE PRINT 12 SX 16 PRINT SX 24 IF MINUTES 10 PRINT 0 SX 32 PRINT MINUTES END Notice that you can set the interval to any number of clock minutes and that you can set the speed with DELAY Try running CLOCK 300 5 22 30 Next we give another colorful design TO SPIDER X COLORSET 1 0 REPEAT 36 HATCH 1 OFFSET X C MAKE C C 1 RT 10 VANISH END TO OFFSET LENGTH COLOR
21. also like to thank our children Aaron Jenell and Kirstin whose responses to early versions of Color LOGO convinced us that we were on the right track ae he ld George Gerhold ny Maly Larry Kheriaty iii Table of Contents Introduction AA RUE E VA E ES 1 1 A Bit About Color LOGO is fib ae tt AR re a 3 2 Getting Started sc sn ar a 5 3 Modes and Editing 2 2522 2 2 55 5 13 Ay PIoGGQUEOS are an 17 5 Repeatand 21 Variables seat il 27 12 OO reellen 31 8 Other Turtle 35 9 Saving Loading and Printing Procedures 39 10 Recursion urn ed 5 43 11 DOODLE Mode Procedures Without Typing 53 12 One Key Doodling 57 13 Useof DOODLE Mode and OK 61 14 Multiple Turtles vada ai 71 15 New Shapes for Turtles sat 81 89 17 Grab Bag anne ee 99 Appendix 1 Language 107 Appendix 2 Making a Backup Copy of the Color LOGO Diskette 123 INTRODUCTION Radio Shack Color LOGO is an educational computer language The language can be used to draw pictures on the computer s video display using a shape on the screen called a turtle Color LOGO is designed to let
22. can view create or modify programs RUN MODE is entered from BREAK MODE by pressing the R key In this mode the user can enter turtle commands call programs to be run or enter DOODLE MODE DOODLE MODE is entered from RUN MODE by pressing the 9 key In this mode the user can doodle a picture while creating a procedure using special marked keys BREAK MODE BREAK MODE is entered automatically upon starting Color LOGO and can be entered from any other mode by pressing the BREAK key at any time It is signified by the LOGO prompt on the screen 107 The following commands may be used in BREAK mode SHIFT CLEAR clears the internal program area R enters RUN MODE E enters EDIT MODE prints contents of internal program area on the printer connected to the serial port 91 prints same as P command except the sends a line feed after a return character IL prompts for module designation with LOAD then reads from the specified source into the internal program area To load from tape enter To load from disk enter the module identifier which is a single letter from A to P Both require an ENTER to start The disk version allows program loading from disk or tape The ROM version loads programs only from tape s prompts for the module name with 5 then writes the internal program area to the specified destination To save on tape enter to save on dis
23. in any of the 8 possible directions The 8 directions are up down right left and the four diagonal directions The one letter commands that may be used in a shape list are shown below The shape list can be any length If it runs over a line boundary put a hyphen at the end of the line then continue in column 1 of the next line The turtle shape drawing pen complements the affected pixels That is the complement of dot present is dot present and vice versa This allows a turtle to pass over a picture without destroying the picture 118 TURTLE SHAPE COMMAND MEANING F step forward one pixel if the pen is down complement the pixel B step backward one pixel if the pen is down complement the pixel R rotate right by 45 degrees L rotate left by 45 degrees U pick up the turtle shape pen this pen is always assumed down at the start of a shape list This pen should not be confused with the turtle pen that draws when a FOR WARD or BACK turtle graphics statement is executed D put the turtle shape pen down if the pen was previously up then putting it down will cause the current pixel to be complemented MULTIPLE TURTLES Normally one turtle exists The user can create additional turtles by using the HATCH statement Each turtle then runs its procedures independently of the other turtles The HATCH statement assigns an identification number to each turtle That number may be used by other turtles t
24. in the operation of one computer with the Software but only to the extent the Software allows a backup copy to be made However for TRSDOS Software CUSTOMER is permitted to make a limited number of additional copies for CUSTOMER S own use F CUSTOMER may resell or distribute unmodified copies of the Software provided CUSTOMER has purchased one copy of the Software for each one sold or distributed The provisions of this Software License shall also be applicable to third parties receiving copies of the Software from CUSTOMER copyright notices shall be retained on all copies of the Software V APPLICABILITY OF WARRANTY A The terms and conditions of this Warranty are applicable as between RADIO SHACK and CUSTOMER to either a sale of the Equipment and or Software License to CUSTOMER or to a transaction whereby RADIO SHACK sells or conveys such Equipment to a third party for lease to CUSTOMER B The limitations of liability and Warranty provisions herein shall inure to the benefit of RADIO SHACK the author owner and or licensor of the Software and any manufacturer of the Equipment sold by RADIO SHACK VI STATE LAW RIGHTS The warranties granted herein give the origina CUSTOMER specific legal rights and the original CUSTOMER may have other rights which vary from state to state Radio Shack Color LOGO By Larry Kheriaty and George Gerhold First Edition Color LOGO program 1982 Micropi All Rights Reserved Licensed to T
25. is no question that the turtles slow down as the number of turtles on the screen increases After all more is going on Thus far we haven t had so many that the slowing is that noticeable But how about a program which generates a lot of turtles One interesting test is to return to a recursion program and implement it using multiple turtles TREE is an ideal example Try the following TO TREE S IF ME CLEAR SETY 9 IF S gt 6 FD S LT 30 HATCH 1 TREE 3 5 4 RT 60 HATCH 2 TREE 3 5 4 VANISH END 75 Again we ve introduced a new idea with this procedure here the ME function The ME function returns the identification number of the current turtle The statement IF ME 0 CLEAR SETY 0 says if the current turtle is turtle 0 then clear the screen and move Because turtle is subsequently told to VANISH this will happen only once This procedure recursively hatches new turtles all named either 1 or 2 Because the recursive calls keep levels distinct this is satisfactory but functions like NEAR would give unpredictable results because the various turtles are not uniquely named There are a number of interesting things that can be tried with this procedure One is to compare it in speed with the earlier version of TREE In one case you have all the backing up necessary for a pure recursive program and in the other you have the overhead necessary to keep track of all the turtles To make the comparison meaningful you ll have
26. listing of the procedure from the Screen and clears the screen but it does redraw the shape with the last step now eliminated Try eliminating step after step by repeated use of the left arrow key The edited version of the procedure is stored in the memory in correct form and can be seen in EDIT mode Another type of editing the child may wish to do is to add on to the end of a previous procedure There is no simple way to do exactly that but it is easy to produce the same effect Get into RUN mode and run the current version of the procedure That will draw the shape on the screen Get into DOODLE mode and give a second name Notice that the turtle is at the home position instead of at the end of the shape Start the new procedure with HOME key 2 raise the pen key 3 move to the end of the shape and lower the pen key 4 Now you are ready to proceed with completing the shape To get the whole shape while running either run the two procedures in sequence or in EDIT mode remove the END statement from the first procedures and the TO name statement from the second procedure If you do the latter you can remove all the turtle commands from HOME to PENDOWN at the start of the second procedure as well 94 Thus far we have limited ourselves to horizontal vertical and 45 degree lines What about other angles It might be useful for you to reread the discussion about circles in Chapter 5 at this point There we saw that with a step forward
27. pattern TO PATTERNS CLEAR LINES 60 128 10 HOME END 65 TO LINES LENGTH X STEP IF LENGTH STOP SX X SY 36 5 0 FD LENGTH RT 90 FD LENGTH LINES LENGTH STEP X STEP STEP END The starting points for the pattern are picked so as to center the pattern on the home position Thus because home is at 128 96 the starting point for the first line is at 128 36 which is 60 units below home We ve chosen to orient the pattern so that the child can begin drawing without turning the turtle At some point the child will need practice in learning letters and numbers Part of learning to recognize them is to look at them very carefully and this can be encouraged by use of DOODLE mode activities The child will probably want to use the letters later to write simple words so we ll save the procedures they make The first tasks could be simply copying from a model Because most people identify computers with mathematics here we ll counter that tendency by using letters for examples We ll begin with the letter F We need a procedure to draw the model TO DRAW F CLEAR SX 50 SY 146 RT 180 FD 50 SX 50 SY 146 1790 FD 30 SX 50 SY 126 FD 20 HOME END This will draw a large capital F as you can see by running the procedure However it will draw the F so quickly that it gives the child no hint as to the order in which the lines should be drawn The order can be indicated in several ways Color can be used draw the
28. per line and any number of lines may be used This statement must follow an IF statement If the expression value on the IF statement is false then the list of statements after ELSE is executed Otherwise it is skipped The expression is evaluated if it has a value less than or equal to zero then the list of statements is skipped Otherwise the list of statements is executed the specified number of times The expression is evaluated if it is false 0 then the list of statements is skipped If it is true non zero then the list of statements is executed After the list is executed control returns to the WHILE again The expression is then evaluated again The list of statements is executed repeatedly until the expression is found to be false This terminates the execution of a procedure Control is returned to the calling procedure if there is one If the procedure was called from RUN MODE then control returns to RUN MODE If the procedure was called by a HATCH statement then the associated turtle goes out of existence This statement defines the start of a Color LOGO proce dure It must start in column 1 of a line and must be the only statement on the line The procname may be any name of one or more letters The parameters in the parmlist may be from 0 to 5 variables Each one con sists of a colon lt lt followed by any word of one or more letters END VANISH MAKE var expr PRINT text PRINT expr
29. pressed the command is executed 110 COMMANDS WHICH CAN BE ENTERED DIRECTLY IN RUN MODE CLEAR HOME FORWARD BACK RIGHT LEFT PENUP PENDOWN PENCOLOR SHOWTURTLE HIDETURTLE SETX SETY SETHEADING SLOW COLORSET BACKGROUND WRAP NOWRAP SEND PRINT HATCH VANISH Some of these commands may be abbreviated as shown below Other Color LOGO commands may not be entered in RUN MODE they may only be used within a Color LOGO procedure TO EXECUTE A COLOR LOGO PROCEDURE FROM RUN MODE To run a procedure entered earlier via EDIT or DOODLE MODE just enter the name of the procedure Follow the procedure name with any arguments to be passed to the procedure then press ENTER Each argument is preceded by at least one space An argument can be a number a variable or an expression If an expression is used it must be enclosed in parentheses DOODLE MODE DOODLE MODE is entered from RUN MODE by pressing the key DOODLE MODE allows the creation of a turtle graphics procedure that will draw a shape without requiring that the user even know how to read In DOODLE MODE the screen displays an sign The user enters a word nonsense or otherwise of at least one letter or number and presses ENTER The word is the name of the procedure to be created as a picture is drawn Now the numeric keys marked by the special keyboard overlay can be used to enter turtle graphics commands Each time a key is pressed the specified command is execute
30. procedures The following procedures are typical TOT SHO HT PD FD 8 RT 150 FD 15 TRI 15 SHO FD5 PU ST END 91 TO TRI SIDE IF SIDE lt 2 STOP REPEAT 3 RT 120 FD SIDE TRI SIDE 2 END T will draw a triangle You might wonder why T is so elaborate after all we could use the following to draw a triangle TO QUICKT REPEAT 3 FD 15 RT 129 END The problem here is that the orientation of a triangle drawn by QUICKT will depend on the prior heading of the turtle For the applications we have in mind we want all the triangles to have one vertex pointing up SH 0 We also want to color in the triangle and we want to draw the triangle around the turtle s starting position Therefore we use the procedure TRI and we move forward eight units before starting the triangle hiding the turtle gains speed TRI uses recursion to make a filled in triangle To get complete filling in we must start at the correct vertex of the triangle this is not obvious but is a consequence of the way in which the Color Computer produces color in high resolution Thus the line RT 150 FD 15 in T moves us to a different vertex You might try replacing this line with RT 30 to get a striped triangle and then make TRI read REPEAT 4 RT 129 FD SIDE to get an even more interesting pattern The commands in T after TRI 15 return the turtle to the starting position with a heading of degrees A similar set of procedures can be used to define a square and a c
31. project and think you may want to use some pieces of a previous project load the previous project before you start You can always delete what you don t need from memory and you have plenty of space 41 10 RECURSION In the Color LOGO language any procedure can call any procedure When the procedure calls itself we have a very powerful logical structure called recursion One clever example of recursion was given by Hofstader in his book Godel Escher Bach Hofstader s Law It always takes longer than you expect even when you take into account Hofstader s Law There are actually two types of recursion We ll start with the easier one recursion where the call is the last statement of the procedure As usual it is easiest to look at examples Recursion can be used in place of the REPEAT statement TO CIRCLE FD 3 LT 10 CIRCLE END When we run CIRCLE the turtle moves forward three steps and turns Then CIRCLE is called which causes the turtle to move forward three steps and turn etc In principle this process could continue forever However every time a procedure is called some memory is used up Eventually the memory is all used up and we get the message MY MEMORY IS TOO FULL Try it So although recursion can be used exactly like REPEAT there are some disadvantages to doing this We have to find some way of stopping the computer or it will run out of memory There are also some great advantages to using this t
32. the most complex procedure Another solution to the problem mentioned above is contained in the procedure ABSTRACT TO ABSTRACT CLEAR COLORSET 1 RT 25 HATCH 1 PATH 1 4 30 RT 43 HATCH 2 PATH 2 4 20 RT 67 HATCH 3 PATH 3 4 40 RT 105 HATCH 4 PATH 4 10 VANISH END Notice that turtle 0 is turned between each HATCH The initial position and heading of each new turtle is the same as that of the parent turtle the turtle which hatches the new one In this example turtle 0 is the parent so each new turtle will have the position and heading of turtle 0 at the time of HATCHing After the four new turtles are created then turtle 0 is given the VANISH command The VANISH command tells a turtle to go out of existence Once turtle 0 is out of existence it no longer gets a turn and it cannot bring the procedure to a halt by running out of commands 73 Of course this procedure needs PATH to function TO PATH COLOR 14 HT PC COLOR WHILE 1 FD L RT 90 PU FD l RT 90 PD FD L LT 90 PU FD l LT 90 PD IF NEAR 255 gt 150 RT 108 END tie Rp ety ui 16 y ur r2 AN eS A Bog EES PATH contains some new ideas which we should explain The first is the WHILE statement The WHILE is somewhat like a REPEAT but with a condition The most common use is to repeat while some condition is true for example WHILE X lt 3 The computer evaluates the condition and returns the value zero if the con
33. the same time we create the target at a randomly selected position HATCH 5 TARGET The REPEAT loop actually moves the ball If the ball is close to the first paddle turtle 2 the heading of the ball is changed LT HEADING 4 HEADING 2 180 2 There is a similar change when the ball is close to the second paddle turtle 3 Notice that when the ball has moved the maximum distance it triggers a new ball before disappearing 95 TO LAUNCHBALL HT PU SHAPE UFFRRDFRFRFFRFRFFRFRFFR FRF MAKE Y RANDOM 60 160 END TO STARTSPOT HT SH Y SX 60 SY 180 REPEAT 6 FD 10 WHILE XLOC 4 gt 7 amp YLOC 4 gt 7 FD 10 RT 180 ST FD 10 END LAUNCHBALL creates an appropriate shape for the ball and effectively picks a random starting point by picking the heading STARTSPOT hides the ball turtle locates it at the first paddle moves it until it reaches the edge of the screen and finally turns it around and makes it visible TARGET does the scoring First it picks a random position and creates a target shape Then it watches for a close approach of the ball from below if the ball approaches from above it has not bounced off the second paddle If the ball turtle 4 comes close enough then a message is sent to the scorekeeper and to the ball TO TARGET SH 0 HT SX RANDOM 100 135 SY RANDOM 40 120 SHAPE URRFFFFFFFFFLLLDFFFF FLFFFFFFFFFLFFFFF ST REPEAT 100 IF NEAR 4 lt 15 amp ABS HEADING 4 180 gt 90 SEND 6 1 SEND 4 1
34. to make the two versions draw the same size tree but by now that is easy The comparison may give some idea of why multiprogramming is worth learning about You can speed the multiple turtle version by reducing the number of times the turtle has to be drawn Simply insert a HT command as the first command in the procedure One other change converts the tree into full blossom Try TO TREE S IF ME 0 CLEAR SY 0 IF S gt 6 FD S LT 30 HATCH 1 TREE 3 5 4 RT 60 HATCH 2 TREE 3 5 4 VANISH ELSE REPEAT 500 END The addition is the ELSE statement The ELSE is a partner of the IF statement The combination says if the current value of S is greater than 6 then obey the commands in the following set of parentheses from FD S through VANISH but if S is not greater than 6 then obey the commands in the parentheses following ELSE The commands following ELSE simply delay the completion of the procedure so that we can see the tree with a turtle at the end of each branch 76 Trees are so easy to draw with multiple turtles that we may as well draw a complete forest In fact we ll look at two forests one a deciduous forest in winter and the other an evergreen forest in whatever season you like TO FIR1 N X Y HT SX X SY Y PC BK N 2 RT 90 FD N 4 LT90 FD 6 N 2 RT 90 FIR 11 N X END TO FIR11 N RT 15 FD N LT 129 FD 3 N WHILE XLOC ME gt X FD 2 END TO FIR2 N X Y HT SX X SY Y BK N 2 LT 90 F
35. turtle is heading straight up Then the command SHAPE URRFFFLLDFFFFL FFFLLFFFLFFFF 81 will draw the following turtle shape Notice that the turtle shape commands extend over more than single line Multiple lines must be connected with a hyphen and must start in column 1 This in turn means that there is no limit on the size or complexity of a turtle shape However the turtle shape must be redrawn every time the turtle moves so the larger and more complex the turtle shape the slower the system will run It is fairly difficult to create desired turtle shapes by trial and error at the keyboard It is especially difficult to locate an error in the middle of a string of turtle shape commands We have found the following to be effective ways to proceed First design the turtle shape on a piece of graph or engineering paper The possibility of rotating the paper as you enter the shape may save you from getting a stiff neck trying to play turtle at the keyboard Once the shape is designed on the graph paper there are two methods which we use If the turtle shape is a simple one enter the shape in DOODLE mode Remember that the keys 8 4 5 6 and 7 correspond exactly to the turtle shape commands U D R L and F Only B is missing and while B is very useful it is not essential Use of DOODLE mode continually shows you the current heading which is a big help However the turtle drawn in DOODLE mode will not lo
36. 48 12 END TO NPOLY N S C PC C REPEAT N POLYGON N S RT 360 N END TO POLYGON N S REPEAT N FD S RT 360 N END TO N2POLY N S1 S2 1 HT PU MAKE 11 WHILE 1 lt HATCH I NPOLY N S2 1 1 1 2 2 FD S1 RT 360 N MAKE I 1 1 VANISH END 105 Of course you can try this set with other inputs than those given in SAMPLE Well we have now reached the point where you are on your own We are sure that the examples herein have just scratched the surface of what is possible We hope that you have as much enjoyment working out your own demonstration procedures as we have had in developing these 106 APPENDIX 1 LANGUAGE SUMMARY OF MICROPI COLOR LOGO FOR THE RADIO SHACK COLOR COMPUTER STARTING LOGO From Plug in ROM Plug the Color LOGO cartridge into the game slot then turn on the computer From Disk Put disk in drive 0 type LOADM LOGO and press the ENTER key wait for the drive light to go out type EXEC and press ENTER MODES IN COLOR LOGO The Color LOGO system can be in one of 4 modes depending upon what the user is doing at the time A brief explanation of each is given here BREAK MODE is entered upon system startup and by pressing at any time In this mode the user can load and or save programs from tape or diskette make printed copies of programs or get into EDIT or RUN modes EDIT MODE is entered from BREAK MODE by pressing the E key In this mode the user
37. BOX to get an estimate of the angle and distance remember press BREAK then press R then enter BOX The turtle needs to be turned more than 90 degrees to point along the diagonal Make a guess and return to EDIT mode BREAK E Now place the cursor under the E in END hold down and press This inserts a blank line try the up arrow key to check that END has just been bumped down one line You can now insert your RT and FD commands in this new blank line It will no doubt take you several tries to get the angle and length exactly right that will give you good practice in bouncing back and forth between RUN and EDIT modes No fair using your knowledge of trigonometry with turtles you are supposed to experiment In this chapter we have covered two main topics We have learned how to enter and change multiple command procedures and we have learned how to teach the turtle to understand more complex commands via procedures 19 5 REPEAT AND SUBPROCEDURES Once we have taught the turtle a new word by writing a procedure we can use that new word in further procedures Return to EDIT mode and remove the commands for drawing the diagonal I used RT 122 FD 59 from BOX Now move to a new line press ENTER In fact a blank line between procedures will help keep things easy to read so press again We re going to write another procedure to draw the pattern of four boxes We ll call it FOUR so type TO FOUR B
38. Cat No 26 2722 THIS WARRANTY SUPERSEDES ALL PRIOR WARRANTIES TERMS AND CONDITIONS OF SALE AND LICENSE OF RADIO SHACK COMPUTER EQUIPMENT AND SOFTWARE PURCHASED FROM A RADIO SHACK COMPANY OWNED COMPUTER CENTER RETAIL STORE OR FROM A RADIO SHACK FRANCHISEE OR DEALER AT ITS AUTHORIZED LOCATION LIMITED WARRANTY I CUSTOMER OBLIGATIONS A CUSTOMER assumes full responsibility that this Radio Shack computer hardware purchased the Equipment and any copies of Radio Shack software included with the Equipment or licensed separately the Software meets the specifications capacity capabilities versatility and other requirements of CUSTOMER B CUSTOMER assumes full responsibility for the condition and effectiveness of the operating environment in which the Equipment and Software are to function and for its installation RADIO SHACK LIMITED WARRANTIES AND CONDITIONS OF SALE A For a period of ninety 90 calendar days from the date of the Radio Shack sales document received upon purchase of the Equipment RADIO SHACK warrants to the original CUSTOMER that the Equipment and the medium upon which the Software is stored is free from manufacturing defects THIS WARRANTY IS ONLY APPLICABLE TO PURCHASES OF RADIO SHACK EQUIPMENT BY THE ORIGINAL CUSTOMER FROM RADIOSHACK COMPANY OWNED COMPUTER CENTERS RETAIL STORES AND FROM RADIO SHACK FRANCHISEES AND DEALERS AT ITS AUTHORIZED LOCATION The warranty is void if the Equipment s case or cabinet ha
39. D N 4 RT 90 FD 6 N 2 LT 90 FIR22 N X END TO FIR22 N X PC 1 LT 15 FD N RT 129 FD 3 N WHILE XLOC ME lt X FD 2 END TO FIR N X Y T HT HATCH T FIR1 N X Y HATCH T 1 FIR2 N X Y IF N gt 20 STOP FIR N 1 X Y T END TO EVERGREEN TREES HT WHILE TREES gt 0 MAKE X RANDOM 200 20 MAKE Y RANDOM 100 30 MAKE T TREES 3 HATCH T FIR 2 X Y T REPEAT 30 MAKE TREES TREES 1 VANISH END 77 5 Try running this set of procedures first with one tree and then with several With some TV sets you may be able to get green tops and brown trunks so try playing around If not you can always claim that they re intended to be blue spruce There are a couple of new ideas in the last two procedures In FIR11 we have used the XLOC function This returns the X screen coordinate of the designated turtle Here X is the starting point for the right half of the tree When XLOC has returned to the starting point the procedure is finished In FIR notice the use of the variable T to indicate the turtle number In EVERGREEN we have introduced the RANDOM function RANDOM produces a random number between 0 and the argument 1 For example RANDOM 200 20 adds 20 to a random number between and 199 The result must be a number between 20 and 219 We do this to keep the trees away from the edge where the wrap around will give some rather lopsided trees Also note the use of WHILE in co
40. DLE mode procedures Also notice that the character has a special meaning in EDIT mode If you want to include an character in a line of a procedure to prevent a line feed when printing you must press O twice a row 55 12 ONE KEY DOODLING The idea of DOODLE mode can be extended to an open ended set of single keystroke operations if we give up the ability to store and edit the child s input as a procedure This requires a set of procedures which we hereafter refer to as the OK Set One Key Set To start we define a set of procedures with single character names Then pressing the single key and ENTER will call forth the desired action This is easier shown than described The first step is to define a set of procedures which match the individual keys in DOODLE mode Because we are not going to save or edit the procedures we do not bother to draw the special symbols at the bottom of the screen although if there was some reason to have them we could draw them with turtle commands Clear the memory and enter the following procedures TO 1 TO 2 CLEAR HOME END END TO3 TO 4 PU PD END END TO5 TO 6 RT 45 LT 45 END END TO 7 TO 8 FD 1 FD 10 END END 09 0 15 15 END END This set of procedures will allow the child to move the turtle freely around the screen in RUN mode using the keys he or she already knows from DOODLE mode The advantages of this approach become evident when we add to the list of
41. END eer 90 113 SIS EB Zen nee eade suas 36 115 SETHEADING 36 115 SEX e es 35 115 SETY cole ieee Berufs 35 115 SEL its e e e ERU 36 SHAPE a ER 81 115 SHOWTURTLE 11 115 er 72 SLOW os O geo ees 73 114 Speed 73 114 SE oe ele A ns ERE A ed 11 115 STOPE Saras ust el 47 112 ee aeo rette tao 23 Subprocedure 2 SM en di see 35 115 OY ee Ce teh re dos a lt gates 35 115 TO ee E 17 112 Turtle 255 05 Mean 91 Turtle 3 110 VANIS He u uen cte Sets 73 113 Variable its 27 116 WATT eg 67 WEILE nn ee 74 112 WRAP ee N ee da 44 118 Wrap around 44 113 rl N 78 117 NOC Are 78 117 2 BAR RU 338
42. GO Try triangles pentagons hexagons threes and fives instead of just boxes and fours Here is another sample TO DIAMOND FD 50 LT 45 FD 50 LT 135 FD 50 LT 45 FD 50 END TO DIAMOND2 REPEAT 29 DIAMOND RT 49 END 22 Color LOGO is a structured language A complex program written in Color LOGO could have the following structure Each letter within a box represents a procedure each line of type on the page includes the subprocedures of a particular level the lines indicate which subprocedures are used by each procedure There are four levels of procedures within this program The master procedure A level 0 might use the subprocedures of level 1 in the order B C D C Subprocedure B might use the subprocedures of level 2 in the order E F E subprocedure C might use the subprocedures of level 2 in the order G F H etc Notice that subprocedures can be used many times and many places within the overall program Thus far in our examples we have been working from the bottom up defining a first procedure then writing a second procedure that uses the first procedure as a subprocedure etc That is typical of programming manuals where the emphasis is on the mechanics of a language instead of on problem solving It is especially fun to adopt that approach with Color LOGO at times because the results are often unpredictable and interesting However as we become more serious we often will have a problem we wish to solve Then we s
43. K RIGHT and LEFT Next we want to combine these commands into a unit which we call a procedure The first step is to tell the computer not to obey each command as it is typed but to store the commands This is what happens in EDIT mode Press BREAK then hold SHIFT down and press to clear the memory of old programs Then get into EDIT mode press The screen should be blank with the cursor in the lower left corner If the screen is not blank return to BREAK mode by pressing the BREAK key hold the SHIFT key down and press the CLEAR key firmly Return to EDIT mode by pressing E You are now using a line oriented editor We will practice using the editor as we create and edit procedures Our first exercise will be to write a procedure for drawing a rectangle First we must give the procedure a name We ll call this first one RECTANGLE The first line of the procedure contains the name and we let the computer know that we re naming a procedure by starting the first line with the keyword TO To name this first procedure RECTANGLE enter TO RECTANGLE The limitations on procedure names are that they must fit on a single line they must contain no spaces and they must not be the same as any of the keywords or abbreviations for example FORWARD or FD If you made a typing error when you were using RUN mode you got the error message DON T KNOW HOW TO followed by your mistyped command Because a p
44. OGO includes a way to change the shape of individual turtles As we shall see this gives us a bonus a way to do simple animation The shape of the turtle is changed by means of the SHAPE statement Following the SHAPE is a list of turtle shape commands Turtle shapes are drawn using a very limited set of turtle graphic commands basically forward and back a single step right or left by 45 degrees and penup and pendown The commands in a SHAPE statement have absolutely no effect on the turtle position heading or pen state The symbols used for these commands are listed in the following table TURTLE SHAPE COMMAND EFFECT F Step forward one dot If the pen is down complement reverse the color of the dot B Step backward one dot If the pen is down complement the dot R Turn right 45 degrees L Turn left 45 degrees U Pick up the turtle shape pen This pen is always down at the start of a SHAPE command The turtle shape pen is completely independent of the standard turtle pen PU and PD commands have no effect on the turtle shape pen and U and D have no effect on the turtle pen D Put the turtle shape pen down If the turtle shape pen was up the putting it down will cause the current dot to be complemented Notice that because the only forward or back possible is one dot then the only turns which make sense are 45 degree turns This will be clearer if we give an example Let us assume that the current orientation of the
45. OX BOX BOX BOX END Notice that we ve used BOX as a turtle command in the same way that we used FORWARD and RIGHT within BOX Run FOUR to see that it works The result is the same as that shown on page 18 To run the procedure FOUR the computer must have available the subprocedure BOX Both procedures must be in the program space when FOUR is run but their order within that space is of no importance We could have written FOUR first and then written BOX with exactly the same result The procedure FOUR can be shortened by use of the REPEAT control statement The altered form of FOUR is TO FOUR REPEAT 4 BOX END The REPEAT tells the turtle to repeat the actions within the parentheses the designated number of times in this case four The space after the number 4 is optional The parentheses can include a whole list of turtle commands and subprocedure names The list in parentheses can extend over many lines but the parentheses are essential Now that we have taught the turtle what FOUR means we can move to a higher level procedure Try TO MANY REPEAT 10 FOUR RT9 END 21 By now you probably are tired of following the manual and are consumed with curiosity What would happen if I changed the number on the REPEAT in MANY what would happen if I changed the angle in MANY what would happen if I restored the commands to draw the diagonal in BOX Don t hesitate to find out by trying that s the whole point of Color LO
46. PER 9 END The names of the procedures for the four turtles are pretty descriptive RUNNER controls the runner and CHASER controls the chaser SCOREKEEPER keeps the score GETKEYS reads input from the keyboard Of course the various turtles need to communicate and that is the main new idea we will illustrate in this example 89 Let s begin with the keyboard TO GETKEYS X HT WHILE 1 MAKE X KEY IF X S SEND 2 1 IF X D SEND 2 45 IF X A SEND 2 315 IF X SEND 3 1 IF X L SEND 45 IF X J SEND 3 315 END First we see a trick we used before the use of WHILE 1 as an effective REPEAT FOREVER The second new item is the KEY function The KEY function looks at the keyboard to see if any key has been pressed If no key has been pressed then KEY returns the value 0 Thus if at the time turtle 1 is executing the statement MAKE X KEY no key is depressed then the variable X is given the value 0 If on the other hand a key is depressed then the variable X is given the ASCII value of the key So the KEY function returns either the ASCII value of the key depressed or if no key is depressed The ASCII value is a number assigned to each key on the keyboard according to an industry wide convention In this procedure we do not have to know what the particular number is because the literal for example S automatically computes the ASCII value as well The next task for this procedure is to
47. RFFFFFFF RRFFUFLLFDLLFFFRRFRRFFFLLFUB LLFFFRRFDFFFFFFF LLFFLFFLLFFRBLBLLFRFRRFFFFF RFRFLFFFLFFFFFFFFLFFFLFRF END TO CRAWL T X Y HT PU SX X SY Y RT 90 REPEAT 100 HATCH 1 1 REPEAT 8 FD2 1 2 REPEAT 8 FD2 IF XLOC ME gt 230 VANISH END 87 TO T1 HT TURTLE1 ST REPEAT 10 END TO T2 TURTLE2 ST REPEAT 19 END TO HERD CLEAR HT MAKE 10 MAKE T1 REPEAT 29 IF 1 lt 10 MAKE 14 1 MAKE J 1 WHILE J lt 1 HATCH T CRAWL T J 18 MAKE T T 2 MAKE J J 1 REPEAT 999 0 END C gt DUNT Roa Ac gt DA It is clear that while much is possible with the turtle shapes Color LOGO is not likely to become a tool for the generation of Saturday morning TV shows It was never intended that it should be so It is a too that will allow the child to produce results which can be immensely satisfying to the creator 88 16 GAMES One of the most popular applications of computers is gaming Color LOGO can be used to create a great variety of games In this chapter we will give two examples of turtle games These are included not as competitors for the local video arcade but as illustrations of some very useful techniques for communication between turtles Before getting into the details of the simple game we re going to use we want to point out a few things which may be obvious Most of the popular video arcade and computer games rely
48. The name of a variable consists of a colon followed by any number of letters and or numbers Variables can be used anywhere numbers can be used in this way procedures can be used for a much wider range of applications A typical use of a variable is the following TO SQUARE SIDE REPEAT 4 FD SIDE RT 90 END If you came here directly from the last chapter then there is another version of SQUARE in memory To clear out the memory press SHIFT CLEAR while you are in BREAK mode Then get into the EDIT mode and enter the new version of SQUARE Now to run SQUARE get into RUN mode and enter SQUARE 49 Because we have listed the variable SIDE on the TO statement we must give a value when we call or use the procedure SQUARE Now try a variety of other numbers for instance SQUARE 69 SQUARE 20 What happens if we forget the number Try SQUARE If we don t provide a number then the computer provides a zero The brief flicker is due to the turtle turning in place while drawing a square with zero length sides Variables can be used in other positions as well Here s another example TO DESIGN LENGTH TIMES REPEAT TIMES SQUARE LENGTH RT 360 TIMES END Enter this and try running it with a few different values of TIMES and LENGTH For example DESIGN 49 24 DESIGN 59 10 27 Long rus The computer keeps track of the variables by the order Because the order in the TO statement for DESIGN is
49. actly the symbols used in its definition We can actually edit S in EDIT mode just as we edit any other procedure For example we can add a diagonal to the box in several ways We can add the type of turtle commands we are already familiar with like RT 45 FD 60 This shows that DOODLE mode turtle commands can be mixed with regular turtle commands However in some sense this way of editing defeats the purpose of DOODLE mode as the child is not likely to be able to understand the change To keep it understandable for the child we edit using the DOODLE mode symbols in EDIT mode Each DOODLE mode symbol can be made by pressing followed by the appropriate key Thus we could insert the above instructions for a diagonal by the series of keystrokes 95 08 08 08 08 08 08 That is an RT 45 5 followed by six FD 10 s 8 Try it Obviously this kind of editing would be most useful in a cooperative project where the child was using DOODLE mode and the helper was using EDIT mode A more likely type of error correction or editing is to make changes during the doodling process For example I should not have taken that last step forward or I should not have turned that far To see how to handle this get into DOODLE mode BREAK and enter a new name say B Now doodle out a box but go one step too far on the last side Left arrow backspace will now erase the last step in the procedure Unfortunately it also erases the
50. ame controllers The object of the game is to bounce a ball off two turnable paddles onto a target Here we ll need a few more turtles We first assign four tasks reading of the two controllers a scorekeeper and a trigger to start the whole thing off TO REBOUND CLEAR HT HATCH 2 PADDLE1 HATCH 3 PADDLE2 HATCH 6 SCOREKEEP TRIGGER END 93 Let s look at the paddle controls first TO PADDLE1 HT SX 60 SY 180 TURN 0 END TO TURN P X WHILE 1 MAKE X PADDLE P 2 LINE 3 SH 45 3 X LINE 0 WHILE PADDLE P 2 X END TO LINE COLOR PC COLOR FD 15 BK 15 BK 15 FD 15 END PADDLE1 establishes the position of the first paddle on the screen It calls TURN which actually reads the game controller The new idea in TURN is the use of the PADDLE function The PADDLE function returns a number between 0 and 63 for the designated input the number depends on the position of the controller handle The inputs are 0 and 1 for the horizontal and vertical positions of the left game controller and 2 and 8 for the horizontal and vertical positions of the right game controller Thus PADDLE1 by the instruction TURN 0 tells the procedure TURN to read the horizontal position of the left controller left refers to the position of the plug on the rear of the Color Computer Because the instruction is MAKE X PADDLE P 2 the variable X is a number between 0 and 31 This division of the controller reading by 2 reduces the sensitivity o
51. andy Corporation Color LOGO manual 1982 Micropi All Rights Reserved Licensed to Tandy Corporation Reproduction or use without express written permission from Micropi and Tandy Corporation of any portion of this manual is prohibited While reasonable efforts have been taken in the preparation of this manual to assure its accuracy Micropi and Tandy Corporation assume no liability resulting from any errors or omissions in this manual or from the use of the information obtained herein Please refer to the Software License in the front of this manual for limitations on the use and reproduction of this Software package Foreword For more than a decade the authors have been involved in the use of computers in education and particularly with Computer Assisted Instruction Our experience made us aware of the problems of getting students started right in programming and of LOGO s potential to help solve that problem and we determined that it would be worthwhile to develop a version of LOGO which ran on low cost hardware and allowed relatively long sets of procedures A review of the features of other versions of LOGO revealed that list processing features were not used in most applications List processing was therefore eliminated allowing the design objectives to be met and allowing the addition of some features notably multiple turtles Our debt to the original designers of the LOGO language is acknowledged in Chapter 1 We would
52. any new disk of Color LOGO programs No diskette labels are likely to be large enough for you to indicate all the procedures on disk and it is a poor idea to write on labels once they are on the disk Make sure that you write the disk name on both the card and the disk label before they have a chance to get separated One reasonable format is Disk Name A gt I B S J C K D Z L oido 2 3 N 2 o O H P Loading programs from cassette and diskette is also simple Again it is necessary to be in BREAK mode In response to the BREAK mode prompt press L The prompt then will read LOGO LOAD _ The responses here are exactly the same as for SAVE use letters A through P to load a disk module and T to load from tape In both cases pressing ENTER will start the process Of course with the cassette tape you will have to have the volume set to about 5 have the tape rewound and have the PLAY button depressed before pressing ENTER 40 If you have a printer for your Color Computer you can print all the procedures in memory Again it is all or nothing except that you can interrupt the printing by pressing BREAK without damaging or losing the programs in memory To print connect the printer as described in the Owner s Manual load the paper and turn on the printer From BREAK mode enter P for single space Q for double space and the p
53. arting point We ll use DOT in later examples Next we draw some very simple repeating pattern on the upper row of dots We ll use DOTS in the pattern drawing procedure Several examples follow TO PATTERN1 DOTS SX5 SY 150 REPEAT 10 PD FD 12 PU FD 12 SX5 SY 50 ST PD END Try running PATTERN The idea is that the child is to reproduce the pattern on the upper set of dots on the lower set and then after that is mastered the child is to give an equivalent pattern with some other shapes Before you try this with a child try it yourself Try to copy the pattern on the lower row of dots You ll find that it is more difficult than necessary It is needlessly difficult to move the turtle the correct number of units 12 as the procedure is written We can make the exercise much less bothersome by some minor adjustments Notice that these adjustments in no way detract from the point of the exercise which is to recognize and continue the pattern TO LINE OF DOTS REPEAT 12 DOT FD 20 END The change to FD 20 means that the child can connect dots with two keystrokes key 8 producing FD 10 on each stroke We have to adjust PATTERN1 as well 62 TO PATTERN1 DOTS SX 5 SY 150 REPEAT 6 PD FD 29 PU FD 20 SX 5 SY 50 ST PD END fi gt m m m we You may be wondering we didn t just give you the final versions immediately The point is that we hope you will try creating your own exercises and we want you to see that a little atten
54. ast check we get back into EDIT mode press E To get the whole note on the screen without memory If we want to interrupt this process just press any key to stop the scan To restart the scan press S HIFT 4 again To jump back to the start of the text press CLEAR That is all there is to using the editor We suggest that you practice a bit with it so that when we return to Color LOGO you can concentrate on the language and not have to worry about the mechanies of the editor To conclude this chapter we give a summary of the editing features To Press get into EDIT mode BREAK E display the next line of text or ENTER YY has no effect at last line LENTER adds line after last line add a line at end ENTER type line of text move text down one line 4 no effect at top line move cursor right gt no effect at line end move cursor left no effect at line start replace character position cursor type over error insert character position cursor SHIFT gt no effect if line full type character delete character position cursor SHIFT 15 insert line break line return to top line scroll or scan through text stop scroll or scan 16 position cursor at start of following line SHIFT position cursor at break point SHIFT CLEAR SHIFT 4 press any key 4 PROCEDURES You ve now mastered five primitive turtle commands CLEAR FORWARD BAC
55. ause the following TO statement automatically ends each procedure These procedures actually prevent the message I DON T KNOW HOW TO if the child accidentally presses an unlabeled key In this chapter we have introduced the idea of building shapes or complex picture elements which the young child can call forth with single keystrokes The examples we have given are simple but the only limit to what is possible is your time and imagination Let s now start thinking about ways to use these tools with very young children 60 13 USE OF DOODLE MODE AND OK SET In the previous chapters we covered the operations of the DOODLE mode and the OK Set What is possible and what is worthwhile are two separate questions In this chapter we will pass along some suggestions Our suggestions are aimed at the adult who is working with small children We have collected ideas from a number of sources However we should make it clear that because Color LOGO offers possibilities for working with much younger children than could be reached previously no one at this time really knows what is possible or what is most beneficial Also remember that this is a user s manual for a computer language not a textbook on early childhood education Don t be hesitant to question our suggestions and don t hesitate to try out new ideas Perhaps the best way to start with very young children is to let them play By play we mean to allow them to explore the effects of
56. cedures 28 DESIGN contains our first example of arithmetic expressions here 360 N Color LOGO allows the standard four arithmetic operations addition subtraction multiplication and division No parentheses are needed unless the order of operations is non standard Fractional parts of numbers are dropped Thus in Color LOGO 5 3 1 2 394 4 10 2 8 4 14 Numbers in the range 32768 to 32767 can be handled To throw away the sign of a number use the ABS function ABS 10 is 10 The following procedures give additional examples of the use of variables and arithmetic expressions TO SQUIGGLE FD 7 REPEAT 8 FD 4 RT 45 FD 7 REPEAT 8 FD 4 LT 45 FD 7 END TO SQUIGGLEB SIDE ANGLE REPEAT 360 ANGLE REPEAT SIDE SQUIGGLE RT ANGLE REPEAT 360 ANGLE REPEAT SIDE SQUIGGLE LT ANGLE END Notice the use of the nested REPEAT twice in SQUIGGLES If ANGLE were 180 and SIDE were 4 then each of the pairs of nested REPEATs will repeat 2 4 or 8 times Try SQUIGGLE8 1 20 SQUIGGLE8 3 60 SQUIGGLE8 4 90 29 gt 3Y QUVEGELES 3 66 30 7 COLORS Turtle tracks can be colored and they can change color Your TRS 80 Color Computer offers two color sets or settings in the high resolution screen on which turtles live Thus far you have been running in color set 0 You can shift color sets by the COLORSET command Get into the RUN mode and e
57. children learn by exploring Children plan an action then enter simple commands that move the turtle forward or back or turn it in any direction Here are a few of the special features of Color LOGO e ine oriented editing allows you to write and save sequences of turtle movements called procedures e doodle mode lets children who are too young to read or type accurately use the program e A SLOW command lets you control how fast the turtle moves e Screen colors can be changed e Limited animation is possible with Color LOGO e Variables and arithmetic expressions can be used in the sets of turtle movements that you write and save Color LOGO is a language for beginners For this reason the Color LOGO manual has been written to guide you through use of the language step by step with many examples and illustrations Here is a summary of the organization of the manual 1 Chapters 1 through 10 introduce turtle graphics and the LOGO syntax Readers who are already familiar with LOGO may wish to skim these chapters or to bypass them in favor of the language summary in Appendix 1 2 Chapters 11 through 17 cover features unique to Color LOGO a Chapters 11 through 13 provide hints for using Color LOGO with very young children b Chapters 14 through 16 introduce the use of multiple turtles and new turtle shapes c Chapter 17 contains sample sets of turtle movements that you may wish to explore This Radio Shack Colo
58. ching the turtle to write in handwriting The key is to name each procedure for drawing a cursive letter with that single letter as the name Thus cursive a should be given the procedure name A cursive b the procedure name B etc Then in RUN mode every time a letter is typed followed by ENTER the cursive letter will be drawn Or one could define a procedure with a word spelled out spaces between the letters and the result would be the word in cursive letters TO CURSIVE CAT END will write cat in cursive if the procedures C A and T are correctly defined To make it all work smoothly the turtle will have to end up in the right position after each letter If that is not enough of a challenge then how about making the computer draw letters as they appear in a manual on calligraphy No doubt you will have to make them a bit bigger to get the desired effect The only limitation is that you can t have both upper and lower case letters at once There are limits even with Color LOGO This chapter has given some idea of what can be done with the OK Set and DOODLE mode At this point there are several ways you might continue with a child One is to continue with DOODLE mode giving them even more challenging tasks or encouraging them to create useful procedures which you help them use in RUN mode If they are reasonably good with the keyboard they may not need much help An alternative is to teach them how to extend the OK Set by adding proced
59. d by the turtle At the same time a procedure is created in the program area This procedure can be viewed by entering EDIT MODE When entering commands the BACKSPACE key can be used to erase the last command In this case the entire screen is erased and the shape is re drawn without the last entered command To exit the DOODLE MODE press A procedure created in DOODLE MODE can be called out from RUN MODE to re draw the picture again To do so just enter the name that was given when DOODLE MODE was entered The DOODLE MODE commands are 1 CLEAR 2 HOME 3 PU 4 PD 5 RT 45 6 LT 45 7 FD1 8 FD 10 9 RT 15 0 LT 15 111 COLOR LOGO STATEMENTS AND COMMANDS CONTROL STATEMENTS IF expr list of statements ELSE list of statements REPEAT expr list of statements WHILE expr list of statements STOP TO procname parmlist 112 The expression is evaluated If the value is true non zero the list of statements in parentheses is executed If it is false 0 then the list of statements is skipped The word THEN may be inserted after the expression if desired The IF statement may be followed by an ELSE statement The list of statements denoted here and below see ELSE REPEAT and WHILE consists of zero or more statements enclosed in parentheses The state ments may include any turtle commands or other control statements except the TO statement There may be multiple statements
60. de For example TO DOUBLE SETX 60 MANY 90 SETX 180 MANY 90 END 35 The heading of the turtle also can be set to an absolute value independent of its current heading The command is SETHEADING abbreviated SH or SETH The heading can be anything between 0 and 359 degrees Zero degrees is straight up Try TO DOUBLE HT SX 60 MANY 90 SX 180 5 0 MANY 90 END The remaining turtle instruction is HOME HOME returns the turtle to the home position the center of the screen with a heading of degrees straight up Procedures which draw circles and parts of circles arcs are very useful in other projects There are some drawbacks to the CIRCLE procedure given in Chapter 5 page 25 It s hard to predict the size of the circle from the size of the step it s hard to find the optimum number of steps for the best circle and it s hard to figure where the circle is centered The following procedures are a useful alternate set ARC Y RADIUS DEGREE PU SX X SY Y REPEAT DEGREE FD RADIUS DOT BK RADIUS RT 1 END TO DOT PD FD 1 BK 1 PU END These are slower than CIRCLE but they give the most accurate circles which can be drawn on the screen With some values of RADIUS you might be able to get the same accuracy with fewer steps for example REPEAT 180 and RT 2 but then the number of degrees will have to be divided to get the right number on the REPEAT You also might want to enlarge the dots TO DOT RT90
61. difficult color coding the dots into two or three sets or adding intermediate dots may help The ability to visualize how things will appear in other positions may be worth developing The idea here is to give a figure in one position and to ask the child to doodle it in another position We are going to reuse the child s procedure for final comparison so here we use DOODLE mode One task is to ask the child to complete a partially drawn figure but in another position TO PATTERN6 RT 180 SX 70 FD 50 RT90 FD20 RT 90 FD 20 LT90 FD10 RT90 FD 10 1790 FD10 1790 FD 10 RT 90 FD 10 LT 90 FD20 RT90 FD 20 RT 90 FD 50 RT90 FD 70 SX 198 SY 96 SH 180 FD 50 RT 90 FD70 90 FD 50 END PATTERNS 68 Remember that in entering DOODLE mode it will be necessary to name the procedure that the child is creating The comparison of the two figures can be made nicely Let s assume that the child s procedure is named ZZ After ZZ is completed enter RUN mode and do the following RT 180 PATTERN6 SX 70 SY 146 PC 2 22 This will rotate the original figure and draw the child s figure over the rotated original in another color The result will be even more satisfying when the child is drawing the whole figure in the new position Of course the above set of instructions could be combined into another procedure so as to speed the comparison The DOODLE mode projects can become quite complex For example a long DOODLE mode project could be tea
62. dition is false or a non zero value if the condition is true Here we want it to repeat forever so we assign the condition the value 1 which always is interpreted as true The parentheses following the WHILE enclose the commands which are to be repeated The other new idea is the use of the NEAR function The NEAR function returns an indication of the distance from the current turtle to the designated turtle Actually what you get is the total of the steps in the x direction and in the y direction to the designated turtle In PATH the statement is IF NEAR 255 gt 150 RT 108 The current turtle remember 1 2 8 or 4 is asking the distance to turtle 255 But turtle 255 does not exist When you request the distance to a non existent turtle you get the distance to the home position Therefore this statement says if the current turtle is more than 150 steps away from home then turn right 108 degrees After such a long explanation we should get a program which runs a long time ABSTRACT will surely fit the bill it will run until you hit the BREAK key or until there is a power failure 74 Perhaps you d like a different design TO MIXIT COLORSET 1 BG 0 HATCH 1SWEEP 13 60 30 0 HATCH 2 SWEEP 23 60 160 90 HATCH 3 SWEEP 3 3 190 160 180 HATCH 4 SWEEP 2 3 190 30 270 VANISH END TO SWEEP COL INT X Y H REPEAT 12 HT PC COL SX X SY Y SH H REPEAT 92 INT PD FD 100 PU BK 100 RT INT MAKE COL COL 1 END There
63. e down You may not want turtles that do strange things like that for some purposes You can sometimes avoid it if it is a problem by shifting your point of view For example you might decide that it would be nice to have a turtle which actually looked like a turtle If you draw a side view of the turtle then it will look strange with headings like 180 84 degrees But if you draw a top view of the turtle then it looks fine in any orientation The reason that we drew the stick figure is that we want to show you how to use Color LOGO to do some very simple animation We want to have a figure that will walk We ll need another position for the stick figure so we define another turtle shape The process is the same as before XXX x x x x x x gt x x x x x x x gt lt x gt lt DE PORK x Translating the indicated path into procedure gives TO TWO SHAPE LLURRFFDBBLLFFFFFFRRR FFFRRRFFFFLFFUBBRBBBBRFFFRFD FFFFFFFFFRRRFFFFLLFF UBBLLFFFFLLFDFFFLLFU BLLFFFFLFDFLFRFFRFR FFRFRFFRFRF END Now that we have the shapes we can have some fun First let s make them walk 85 TO WALK HT PU SX 100 RT 90 REPEAT 100 ONE ST WAIT 100 HT FD6 TWO ST WAIT 100 HT FD 6 END TO WAIT T REPEAT T END Notice that in this case we want the turtle shape to be drawn at right angles to the turtle motion That is taken care of in the SHAPE statement Notice also that we have to s
64. e line We decide to change the word STARTING in the second line of the note to the word BEGINNING To do this we must 13 first display the second line and position the cursor under the S in STARTING We move the cursor by use of the arrow keys Up arrow 4 and down arrow 4 change lines and left arrow lt and right arrow gt move the cursor within a line Changing lines always resets the cursor to the start of the line Arrow commands which make no sense are ignored Thus if we press right arrow when the cursor is under the comma following GRANDMA nothing happens because there is no more line To see the second line of the note press the up arrow key once Then press the right arrow key several times to position the cursor under the S in STARTING Then type BEGIN Notice that the overtyping simply replaces the letters Now we have another kind of change to make because BEGINNING has one more letter than STARTING We want space for another N before the ING To create a space we hold down the SHIFT key and press the right arrow key Now we can type the extra N in the created space Remember to insert press SHIFT gt to create the space then type in what you want Next let s change the line from BEGINNING TO USE AN EDITOR I M LEARNING TO USE AN EDITOR Again position the cursor at the start of BEGINNING and type over the characters you want to change Here the problem is that an
65. e the message INSERT DESTINATION DISKETTE AND PRESS ENTER remove the Color LOGO diskette called the SOURCE diskette from the disk drive Insert the new diskette that you used in Step 3 the DESTINATION diskette into the disk drive Close the disk drive latch Finally press ENTER When you see the message INSERT SOURCE DISKETTE AND PRESS ENTER remove the DESTINATION diskette from the disk drive insert the Color LOGO diskette close the disk drive latch and press ENTER Continue to switch between the SOURCE diskette and the DESTINATION diskette as instructed by the computer When the BACKUP process is complete you ll see the prompt reappear 123 Two Drive TRS 80 Color Computer Disk System 1 124 Make sure that the Color Computer is properly connected to the color television or color video Plug the Color Computer Disk Controller into the slot on the right side of the computer Turn the color video and the Color Computer system on The computer s power switch is on the back left corner of the computer The disk drive switch is on the back of the drive in the upper corner Insert a new blank diskette into Drive 1 the disk drive second from the Color Computer on the cable Close the disk drive latch DJ S K 1 NJ and press ENTER Place an adhesive tab provided with new diskettes over the square notch in the Color LOGO program diskette If you do not have a
66. ed by the prompt which ends LOGO at the left of the screen You can return to BREAK mode at any time by any one of three actions 1 key will interrupt whatever you are doing and return to BREAK mode 2 Reset button located on the right rear corner of the computer will always return you to BREAK mode but you will lose all programs in memory 3 A complete restart as described above will place you in BREAK mode BREAK mode will be covered in detail in Chapters 3 and 9 for now let s move into RUN mode by pressing R There is the turtle sitting in the center of the screen facing straight up Admittedly this turtle does not bear a strong resemblance to the ordinary pond type turtle but like an ordinary turtle it can crawl forwards and backwards it can turn right and left Unlike ordinary turtles computerized turtles can drag their tails to leave tracks in colors or raise their tails and not leave tracks Turtles can even be made invisible The name turtle was given originally to a tiny mechanical robot which could be made to crawl around the floor under computer control The name probably had much more to do with the speed of the robot than with the shape of the robot The track left by the turtle was called a turtle graphic The term turtle graphics is now used to indicate a way of drawing where lines are described by a direction and a length the alternative is to describe a line by giving the coordinat
67. ement then that variable is said to be a LOCAL variable That is each time the procedure is invoked a new storage location is assigned to the variable Thus if a procedure is invoked recursively or by several turtles at once then each invocation has its own set of local variables which though they have the same name are kept distinct There may be up to 5 parameters on a TO statement thus there may be up to 5 local variables in a procedure If a variable is referenced in a procedure but is not on the TO statement for the procedure then the variable is said to be a GLOBAL variable There is only one storage location assigned to each particular global variable Thus all references to the global variable refer to the same storage location even if the references are in different procedures This provides a way of sharing information among procedures or among turtles LITERALS C A quote followed by one character is called a literal It can be used anywhere a number can be used The value of a literal is the ASCII value of the character For example A is equal to 65 A literal is particularly useful in checking for values returned by the KEY function 116 FUNCTIONS ME KEY ABS arg RANDOM arg XLOC arg YLOC arg HEADING arg NEAR arg MAIL arg returns the identification of the current turtle The main turtle is number 0 The others are numbered from 1 to 254 returns 0 if no key is depressed If a key is depres
68. en enter commands like FD 20 and RT 90 Remember that the turtle can be drawn in eight positions Be sure to try the diagonal positions for example RT 45 because there will be some change in shape as the turtle rotates to these positions To see why that is so return to the graph paper and follow your turtle instructions beginning along a diagonal It is a good idea to do this on graph paper before going to the computer as your turtle shapes might come apart upon rotation if they are drawn in the wrong sequence To show you that it can happen try the following We could have drawn essentially the same shape by the steps FFFFFRRUFFDLLLFFLLFF in the vertical or horizontal positions but in the diagonal positions this pattern comes apart as you can see if you follow the instructions on graph paper Now we move to a bit more complex example an outline of a plane The dot pattern is X X X X X XXXXXX X XXXXXXX XXXXXXX XXXXXXX and the procedure created DOODLE mode and translated in EDIT mode is TO PLANE SHAPE RRFFFLLFLLFRFR FFFFFFRRFFFFFFF LFLLFLFFFFFFFRRF FLFLLFLFFRRFFFF FFFLFLLFLFFFFFF FRRFFFFFFRFRFLL FLLFF END When we go to more complex shapes we prefer to work with paper rather than with DOODLE 83 mode There are several reasons for this One is that the B command is very useful The other is that we must be very careful if we are to avoid problems when the turtle shape is turned to the 45 degree posi
69. enter another WHILE 1 which will run forever 91 The runner turtle now checks its mailbox by using the MAIL function The number following MAIL the argument is the number of the turtle that the runner turtle will accept mail from Here turtle 2 the runner turtle is asking for mail from turtle 1 the keyboard turtle If there is no message then MAIL returns the value 0 The statement IF X checks for the value of X If it is 0 then the statements in parentheses are skipped Since the parentheses enclose all the rest of the commands a 0 causes the loop to start again Thus the turtle just keeps checking its mail until it gets a message from turtle 1 If we look back at GETKEYS we see that a message 1 meant to move Therefore if X 1 runner is moved forward 8 If at this point the message is not 1 then it must be either 45 or 315 The runner is turned right by either amount remember that RT 315 is the same as LT 45 This completes the move so the turtle goes back to checking its mail from turtle 1 Before going further look carefully at the arrangement of the two IF statements in RUNNER Notice that the parentheses after the first IF enclose the second IF and the ELSE This pairs the ELSE with the second IF The meaning is if X is not 0 the first IF then do one or the other of the following if X is 1 move forward otherwise turn The CHASER procedure is similar to RUNNER but it includes the test for a successful catch
70. error tape checksum error probably a bad tape or the volume not set correctly attempt to load a tape that is not a Color LOGO program attempt to load a module that is too long for memory disk drive not ready or an attempt to write on a write protected diskette or an improperly formatted diskette In RUN MODE there are several possible messages that may be issued These messages attempt to identify the error in the program but remember that the message is only a guess as to what is wrong It is possible that the message does not exactly fit the problem Each time one of the following messages is displayed the user must press any key to continue MESSAGE DON T KNOW HOWTO I CAN T FIGURE OUT I DON T KNOW HOW MUCH 120 PROBABLE MEANING is filled in with the name of what Color LOGO thought was a procedure name to call but the procedure name is not found in the program area If the name is one which should be in the program area make sure that it is preceded by not 0 zero Also make sure TO is in column 1 Check also that the name is cor rectly spelled If the name was not supposed to be a pro cedure then probably there is something wrong with the immediately preceding command is filled in with the word that caused the confusion Color LOGO was attempting to compute the value of an expression when it encountered the problem Possibly the syntax of the express
71. es of programs on disk format a second disk while you re at it Once you get the OK response you can reload Color LOGO as covered in Chapter 2 and reload your procedures from tape as described below A disk for Color LOGO programs is divided into 16 modules Each module occupies 2 tracks or 36 sectors so the capacity of a module is 9K It is doubtful whether you will ever come very close to filling a module with a set of procedures because LOGO procedures tend to be relatively short If you do fill the 9K the editor will refuse to accept additional text The modules are 39 indexed by the letters A through P To save all the procedures in memory on the disk type one of the letters A through P in response to the BREAK mode prompt LOGO SAVE __ You must press ENTER to start the save While you re at it remove this disk insert the second formatted disk and save the procedures on the same module again press S the module letter and ENTER We have on rare occasions had trouble storing programs on the disk The trouble seems to be related to the relative positions of the disk or the ribbon cable and the TV set Whatever after saving on disk we try reloading the module immediately If the load is not successful we get an error message a 6 followed by a question mark but the procedures are still in memory and so we can try another save without retyping the procedures We suggest that you immediately start an index card for
72. es of the two end points of the line a method called strangely vector graphics The item which moves is called the turtle even when it is just a shape on the screen Color LOGO is a language for controlling turtles We have a turtle in the center of the screen itching for action Let s tell the turtle to move forward Simply type FORWARD 40 Commands or program lines which you are to enter into the computer will be represented by the typeface which you see in FORWARD 40 above Some messages from the computer will also appear in this typeface but the context will make the difference clear FORWARD 40 the screen will show FURMARD See the turtle track It won t be long before you get tired of typing FORWARD all the time so there is an abbreviation which has the same effect Enter the following type it and press FD 10 Try to get a feel for the screen size and resolution Try FD 1 It s almost too little to see Then try with a larger number like FD 100 The turtle moved but it didn t leave a track When the turtle goes off the top of the screen it reenters at the bottom a process which is called wrapping around A turtle can wrap around only by temporarily raising its tail so no track appears for any step where the turtle wraps around NOTE If you forget to leave a space between FORWARD and 40 you ll see the message I DON T KNOW HOW TO FORWARD40 You ll ge
73. experimenting with Color LOGO Again we soon get tired of typing RIGHT so we abbreviate RT Try RT 90 Think right turn for RT Now the turtle points down We re half way to drawing a rectangle so let s finish it Enter FD 40 RT 90 and see if you can finish it Once you ve finished the rectangle by entering FD 50 clear the screen and enter RT 45 FD 50 Just what you expected I hope but now try RT 15 It looks like nothing happened But to check try FD 30 Obviously there is a bend in the line even though the turtle did not appear to turn The turtle knows its heading to the nearest degree and moves accordingly but the turtle shape on the screen turns only in 45 degree steps Thus the turtle shape on the screen points close to but not exactly along the turtle heading This seems inconvenient now but in Chapter 14 we ll find that there are some real benefits of this We want you to notice one very important thing about turtle behavior Clear the screen and enter RT 45 RT 45 This produces the same heading as RT 90 When the turtle is told to turn it turns that far from whatever its current heading is We are telling the turtle how to change its heading we are not telling the turtle to head towards some point In the same way when we tell the turtle to go forward we are telling the turtle how to change its position we are not telling the turtle to go to some point on the screen Thus the position and
74. extra N remains To delete a character or space hold down the SHIFT key and press the left arrow key Try it and remember press SHIFT lt to delete Poor Grandma isn t going to know who the note is from unless we add a line at the end Use the up arrow key to move the cursor as far down as you can It should be at the start of a blank line following the text We want to skip a line before signing the note so press ENTER once Notice that pressing ENTER adds a line at the end But if the cursor is within the text pressing ENTER has the same effect as the up arrow Now space over and sign your name While we are at it we should skip a line after DEAR GRANDMA That is we want to change DEAR GRANDMA I M LEARNING TO USE AN EDITOR LOVE ANN DEAR GRANDMA I M LEARNING TO USE AN EDITOR LOVE ANN 14 Position the cursor at the beginning of the line I M Then hold down the SHIFT key and press the down arrow key Move the cursor down to check that you got what you wanted Remember to insert a new line position the cursor at the start of the following line then press SHIFTI V We want to make one last change We want to change the closing to LOVE ANN We want to break one line into two Position the cursor where you want the break to occur over as shown above This we think is the final form of the note so we exit EDIT mode press BREAK To make a l
75. f the display and speeds response Notice that after the first pass through TURN the procedure looks for a change in the controller setting It stays in the loop WHILE PADDLE P 2 X until there is a change When there is a change it runs through the outer loop which updates X erases the old paddle LINE 3 computes a new heading SH 45 3 X and draws a new paddle LINE Remember that X can be between and 31 so the heading for the paddle can be between 45 and 45 8 81 138 The procedure LINE actually draws the paddles and erases them The BK is broken into two steps so that it exactly duplicates the FD steps this insures a successful erase 94 The second paddle is controlled by the second controller We can use TURN and LINE again TO PADDLE2 HT SX 180 SY 12 TURN 2 END Now we have to create the ball and the target TRIGGER starts a new round TO TRIGGER HT HATCH 4 BALL VANISH END The ball should come from a randomly selected point towards the first paddle The easiest way to do that is to create the ball turtle at the first paddle and to move it invisibly in the randomly selected direction These two tasks will be carried out by the procedures LAUNCHBALL and STARTSPOT TO BALL LAUNCHBALL WHILE MAIL 5 0 STARTSPOT HATCH 5 TARGET REPEAT 45 FD 10 IF NEAR 2 lt 20 FD 10 LT HEADING 4 HEADING 2 180 2 FD 35 IF NEAR 3 25 FD 10 LT HEADING 4 HEADING 3 2 FD 45 TRIGGER END At
76. g the square at the center of a side 24 TO SQUARE REPEAT 4 FD 35 90 FD 35 END Now how do we get the turtle to draw a circle One very good way to figure this out is to play turtle That is walk in a circle and think about what you are doing in terms of turtle commands You ll discover that to make a circle you go forward a little and turn a little until you get all the way around The best circle should be drawn by the following right TO CIRCLE REPEAT 360 FD 1 RT 1 END Wrong This gives an eight sided figure explain why but if you find this confusing for now skip the next paragraph When a turtle moves forward one step it has eight choices of where to go We start with the turtle pointing straight up towards 1 and turn the turtle a small amount say 5 degrees right Clearly the only two choices are to go to square 1 or to square 2 and square 1 is closer to the correct direction than square 2 Because Color LOGO does only integer arithmetic the turtle is now assumed to be in the center of square 1 and the process repeats on the next move With larger steps there are more squares to which the turtle can move and we get a better circle In general avoid combining tiny steps with tiny turns for turtles A reasonable circle can be drawn by the procedure TO CIRCLE REPEAT 36 FD 6 RT 10 END This gives the same problem as the first procedure for the square the circle will not be centered in the square We ca
77. he turtle is not moved The PRINT statement also can be used to print the current value of a variable in the same way Both are used here MAIL 255 is a special version of the MAIL function MAIL 255 will accept messages from all other turtles Here we could use MAIL 3 just as well since turtle 3 is the only one sending messages to the scorekeeper The following line WHILE MAIL 255 9 continues to check until mail is received One useful characteristic of the MAIL function is that like any decent mail system it will collect messages Thus if several messages have collected from one or more sources the MAIL function will deliver the oldest undelivered message and keep the others for future reference A SEND 255 goes onto every turtle s list That message disappears from all lists when one turtle accepts it Now that you have the whole set of procedures in you can try running the game To start it run CATCHEM Just remember that this is an educational experience not pure entertainment You may discover that there is a flaw in the game If the runner is caught close to home then because the chaser is returned to home after each successful catch the runner is unable to escape and the score mounts You could fix this by moving the chaser elsewhere if the runner is too close to home or by just incrementing the x position of the chaser by some large number say 100 after each catch The second game is called REBOUND It makes use of the g
78. heading of the turtle after one of these commands will depend on where the turtle started Thus far we have learned three primitive turtle commands Papert would say three words in turtle talk They are CLEAR FORWARD and RIGHT With these three we can draw any figure which will fit on the screen and which could be drawn on paper without lifting the pencil from the paper You might try drawing a triangle 8 sided figure and a pentagon 5 sided figure for practice If you re like us you don t remember the angles for pentagons so experiment You ve probably noticed that only three lines of instructions are shown at any one time When you type a fourth line the lines scroll up and the top line disappears If you have drawn a turtle track through these three bottom lines the scrolling will mess up the line by scrolling a line segment upwards If you leave the turtle in these three bottom lines while scrolling the turtle will not erase properly when moving to another spot These are minor consequences of some characteristics of the Color Computer which will not trouble us once we get to Chapter 4 For now either avoid moving the turtle into the bottom three lines or press ENTER enough times to scroll away the line and turtle fragments or ignore the fragments We could go a long long way with just RIGHT and FORWARD but LEFT and BACK are useful too Clear the screen and try LEFT 90 We could have used the abbreviation LT fo
79. hould work from the top level down Now we illustrate that process The sample problem is to create the following pattern PRTTER E 23 Obviously the figure is so symmetrical that there is a repeat pattern Furthermore the number of repeats must be six The crucial step is to recognize that the element that is repeated six times is a square with a circle inside Therefore our main procedure should be TO PATTERN REPEAT 6 SQUARE CIRCLE RT 60 END The six fold symmetry tells us to repeat 6 times with turns of 60 as 6 60 360 As yet we have no idea how to draw a square with a circle inside Now we move to the next lower level TO SQUARE CIRCLE SQUARE CIRCLE END Again we break the task into simpler tasks This time the breakdown is obvious you draw a square with a circle inside by drawing a square and then a circle Now we drop down to level 2 The obvious procedure for drawing a square is TO SQUARE REPEAT 4 FD 70 RT 90 END This will draw a square but it will leave us with a problem We also have to draw a circle inside the square and SQUARE leaves the turtle at a corner of the square The corner is an awkward place to start drawing a circle which is to be inside the square This example shows that when procedures are to be used together some attention must be devoted to making them fit The circle and the square touch at the center of a side We choose to make the two procedures fit by starting and endin
80. ion is in error or a colon is left out before a variable name or a function name is misspelled This message means that a command such as RIGHT or FORWARD which should be followed by a number is not followed by a number Either an expression is not pres ent where one should be or the very first item in the ex pression is not valid OR 7 NOT RIGHT A left parenthesis is not found as expected after an IF WHILE or REPEAT expression or after an ELSE Or un balanced parentheses are detected CAN T DO THAT IN THIS MODE A command such as REPEAT other than one of the ones allowed is entered directly from the keyboard in RUN MODE Remember some commands may be exe cuted only within a Color LOGO procedure MY MEMORY IS TOO FULL The internal program and work area is filled This will always happen eventually if a program is allowed to do infinite recursion call itself repeatedly forever In general procedure calls hatching turtles and sending messages consume memory The longer the text in the program area the less available memory for these operations OUT OF BOUNDS The screen has been placed in NOWRAP mode and a turtle has run off the boundaries of the screen FORMAT OF A COLOR LOGO DISK A Color LOGO program disk is formatted with the DSKINI command under BASIC However Color LOGO does not use the BASIC directory Color LOGO divides the diskette into 16 modules named A through P Once a diskette is used under
81. ircle TOS SH 45 HT PD FD 1 RT 45 SQU 14 RT 135 FD 10 SHO PU ST END TO SQU SIDE IF SIDE lt 2 STOP REPEAT 4 RT 90 FD SIDE SQU SIDE 1 END TOC SH 0 HT PD FD 8 RT 90 REPEAT 15 FD 4 RT 24 RT 22 MAKE X 7 REPEAT 7 CIR X RT 90 FD 1 LT 90 MAKE X X 1 RT 135 FD2 SH 0 PU ST END 58 TO CIR STEP REPEAT 8 FD STEP RT 45 END The last line before the END in C restores the turtle to the original position Itis not easy to compute what moves are necessary to reach the original position so we do it by experiment Run C immediately upon entering RUN mode so that the starting position for the turtle is at the home 128 96 position When the procedure has finished do an SX 128 and an SY 96 Watch which way the turtle moves if at all From those moves we can tell what changes must be made in the last line of C to restore the turtle to the original home position With these procedures the child can move the turtle around the screen using the number keys and the child can produce triangles by pressing T squares by pressing S and circles by pressing C But I hear you say this is for children who don t know the letters We suggest that you cover the selected keys with small adhesive labels on which the symbols have been drawn In this example this would mean putting a label with a triangle on the T key a label with a square on the S key and a label with a circle on the C key Of course you could use any other keys i
82. iscussed that before The MAKE statement changes the variable following the MAKE to the value given by the next expression or number For example MAKE X X 40 replaces the starting value of X with a value which is 40 greater 64 Of course not all the tasks using the triangles squares and circles need to be directed towards specific goals Ask the child to create a design or to create a border to the screen Another group of projects can be based on completion of design The screen can be thought of as consisting of four quadrants divided at the home position The idea is to have the turtle draw a pattern in one quadrant and to have the child complete the pattern in the other three quadrants Either DOODLE mode or the OK Set can be used here If you ve included the erase procedures for the DOODLE turtle commands in the OK Set then that set is preferable A simple pattern is TO PATTERN4 CLEAR RT 90 REPEAT 2 FD 60 SX 128 SY 96 RT 45 HOME END We have written the procedure so that it is easy to add lines to make a more elaborate pattern However we recommend that you restrict the patterns to those using angles which are easy to produce in DOODLE mode that is multiples of 15 or 45 degrees We reset the turtle to the home position with the SX and SY instead of with HOME so that the turtle heading is preserved Again the FD should be some multiple of 10 to minimize the number of keystrokes needed This gives a more complex
83. itional statement in FRACTAL with IF N X9 FD N 4 RT 80 FD N LT 160 FD N RT 80 FD N 4 STOP and try FLAKE 150 Another variation is IF N 9 FD N 4 RT 80 FD 2 N LT 160 FD 2 N RT80 FD N 4 STOP 50 and try FLAKE 158 FLAKE 70 Recursion can be used to draw endless space filling patterns The following example is typical TO FOO SIZE LEVEL PARITY HT IF LEVEL 0 STOP LT PARITY 90 FOO SIZE LEVEL 1 PARITY 1 FD SIZE RT PARITY 90 FOO SIZE LEVEL 1 PARITY FD SIZE FOO SIZE LEVEL 1 PARITY RT PARITY 90 FD SIZE FOO SIZE LEVEL 1 PARITY 1 LT PARITY 90 END An appropriate set of numbers is FOO 6 6 1 In this chapter we have tried to give you some ideas for recursive programs However we have just scratched the surface of the designs that are possible Go ahead and experiment and let others know if you discover any new beautiful designs 52 11 DOODLE MODE PROCEDURES WITHOUT TYPING Color LOGO provides a way to enter graphic procedures into the computer without typing the turtle commands like FORWARD and RIGHT The reason for including this feature is to provide a way for children who are not yet able to read or not yet able to type reliably to use the language and to benefit from the practice in structured thinking that the language offers The features of DOODLE mode are arranged with that audience in mind Obviously the children are not going to be able
84. k then under Using the Color LOGO Program Plug In ROM Cartridge Plug the Color LOGO cartridge into the slot on the right side of your TRS 80 computer Check that the label is up and that the cartridge is seated firmly Then turn the power on The power switch is on the back left corner of the computer The screen should display the prompt COLOR LOGO COPYRIGHT 1982 LARRY KHERIATY amp GEORGE GERHOLD ALL RIGHTS RESERVED LICENSED TO TANDY CORP LOGO Disk Plug the Color Computer Disk Controller into the slot on the right side of the computer Then turn the system on The computer power switch is on the back left corner of the computer The disk drive switch is on the back of the drive upper left corner You should see the prompt DISK EXTENDED COLOR BASIC 1 0 COPYRIGHT 1981 BY TANDY UNDER LICENSE FROM MICROSOFT OK Follow these steps 1 Insert the Color LOGO diskette with the square notch up and the label facing right into Drive 0 the drive closest to the Color Computer on the cable 2 Close the disk drive latch 3 Type 7101060 and press ENTER 4 After the light on the disk drive goes out type EIX EJ C and press ENTER The system will now display the prompt shown above under Plug In ROM Cartridge 5 Remove the Color LOGO diskette from the disk drive Using the Color LOGO Program Whichever way you started you should now be in BREAK mode which is indicat
85. k enter the module identifier which is a letter from A to P Both require an ENTER to start The disk version allows program saving to disk or tape The ROM version saves programs only on tape EDIT MODE EDIT MODE is entered from BREAK MODE by pressing E In EDIT MODE one can edit the currently loaded modules To start with a blank program area press SHIFT CLEAR in BREAK MODE before pressing E The editor is very easy to use It works on the principle that what you see is what you get The first line of text if there is one is displayed on the bottom line To enter lines of text just type them on the screen The cursor will always appear on the bottom line but the text may be moved up or down the screen at will The following keys cause special actions to take place ENTER moves the text up one line on the screen or if already on last line then adds a new line to the text end gt moves the text up one line unless already on the last line lt moves the text down one line unless already on the first line 108 e moves the cursor left one character unless already at the beginning of line gt moves the cursor right one character unless at the line end CLEAR moves to the top line of the text SHIFT scrolls the text up continuously until any key is pressed SHIFT inserts a blank line in front of the current line if the cursor is in colum
86. l be executed If the current value of N is 2 or greater then this expression is false and the rest of the statement will be skipped The rest of the statement is placed in parentheses it may consist of many commands and it may extend over many lines The second new item in line 1 is the control statement STOP The STOP statement ends a procedure STOP has the same effect as an END statement but an END statement can appear only at the end of a procedure It will be easier to understand TREE if we make some changes to simplify it Change the condition in line 1 to N lt 18 and change the right turns lines 3 and 7 to 45 and the left turn line 5 to 90 Then run TREE 32 to get a simpler tree TREE 37 The following diagram and table outline the operation of TREE Level O N 32 Level N 24 Level 2 N I8 Level 3 NzI3 47 STEP N START END LINES a 32 0 R45 1 4 b 24 R45 R90 1 4 18 R90 R185 1 4 d 13 R135 R185 1 e 18 R135 R45 5 6 f 13 R45 R45 1 g 18 R45 R90 7 9 h 24 R90 0 5 6 i 18 0 R45 1 4 j 13 R45 R45 1 k 18 R45 L45 5 6 13 L45 L45 1 m 18 L45 0 7 9 n 24 0 R45 7 9 82 R45 L45 5 6 p 24 L45 0 1 4 etc First look at the diagram The program tries to reach the lowest level of the procedure until forced to rise in level by the STOP or the END statement By a method which we will explain in Chapter 14 we can single step the program by running it as follows Type HATCH 1 TREE 32 Now every time you press
87. ll seem to evolve instead of appearing piecemeal At a more serious and abstract level we can use the multiple turtles to illustrate the process of multiprogramming Let s begin by entering a few procedures for the turtles to run Clear the memory and enter TO BOX SIDE X Y SX X SY Y REPEAT 4 FD SIDE RT 99 END TO CIRCLE SIDE X Y SX X SY Y REPEAT 20 FD SIDE RT 18 END Run each of these to verify that they are entered correctly We create new turtles by means of the HATCH command The form of the command is HATCH turtle number procedure for the turtle or to give a specific example HATCH 1 BOX 50 30 60 Here the meaning of HATCH is obvious The following number here 1 is the name or label of the turtle Turtles can be labeled with any number between 1 and 254 Turtle is the master turtle always present even if hidden by an HT command which we have been using exclusively up to now BOX is the name of the procedure which we are telling turtle 1 to run The numbers following BOX are as usual the values to be fed into the local variables within BOX 71 Next we try out a simple multiple turtle program Enter the following TO TEST HATCH 1 BOX 50 30 60 HATCH 2 BOX 40 180 90 HATCH 3 BOX 60 100 90 END Notice that each turtle has its own procedure and its own set of values for the variables Of course several turtles can be using the same procedure but each still has its own current set of values for the va
88. low down the process by including the WAIT instruction Otherwise it runs so fast that we have trouble seeing the shape Try other values for T to vary the speed We can make the figure climb just enter LT 15 before running WALK again We can even make the figure walk in a circle TO WALK AROUND HT PU SX 100 RT 90 REPEAT 100 ONE ST WAIT 100 HT RT 15 FD6 TWO ST WAIT 100 HT RT 15 FD 6 END You may prefer the motion you get with a different control procedure Try this as an alternative to WALK TO WALK1 HT PU SX 100 RT 90 REPEAT 100 HATCH 1 WALKA REPEAT 8 HT FD6 HATCH 1 WALKB REPEAT 8 HT FD6 END TO WALKA HT ONE ST REPEAT 10 END TO WALKB HT TWO ST REPEAT 10 END 86 The trick here is to get the delays that is the REPEATS with empty parentheses synchronized The delays WALK1 must match with the delays in WALKA and WALKB If there is a mismatch one direction the two figures will appear together and if there is a mismatch the other way the motion will be unnecessarily jerky After all this talk about turtles we feel an obligation to actually draw something which looks a bit like a turtle As our last example we give a HERD of turtles b LA TO TURTLE1 SHAPE LL BRRFRRFLLFRRFLLFFFFLBBBRFL FFFRFLBBBUFFFRFDFFFFFRFFF LFRBBBLFRFFFUBBBLFDFFFFFFFF LLFFLFFLLFFRBLBLLFRFRRFFFFF RFRFLFFFLFFFFFFFFLFFFLFRF END TO TURTLE2 SHAPE LL BRRFRRFLLFRRFLLFFFFRRFFUBB LLFDRRFFFLLFFUBLLFDFFR
89. mbination with the MAKE TREES TREES 1 This gives a number which is one less every time through the WHILE loop TREES is used to vary the turtle numbers for each tree drawn The deciduous forest uses the TREE procedure we ve already seen To that we must add TO FOREST BACKGROUND 1 SX 236 REPEAT 3 SY 10 SX XLOC ME 40 HATCH 1 TREE 20 SX XLOC ME 40 HATCH 2 TREE 30 CLOUDS END Use the tree procedure from page 75 78 TO CLOUD SIZE X SETHEADING 90 REPEAT SIZE 6 MAKE X RANDOM SIZE 2 PU FD 2 PD FD SIZE X PU BK SIZE X 2 SY YLOC ME 2 END TO CLOUDS PC 2 SX 10 SY 180 CLOUD 69 SX 100 SY 164 CLOUD 30 SX 198 SY 176 CLOUD 65 END Again in this example we have created many turtles with the same numbers by hatching them recursively The two multiple tree drawings show the two ways in which multiple turtles can be created It makes no difference which way you do it unless you are going to refer to the turtle by number In that case each turtle must have a unique number Notice the statement SX XLOC ME 40 This has the meaning SX XLOC ME 40 not SX XLOC ME 40 79 15 NEW SHAPES FOR TURTLES All turtles are created equal at least they all look the same In the examples we have seen so far that didn t matter but often we want the different turtles to look different For instance it would be impossible to play many games if all the pieces or players looked the same So Color L
90. n O character then no RETURN is output at the end of the line The result will be that the following line on the screen will be printed on the same printer line 109 INTERNAL PROGRAM AREA Color LOGO procedures are entered in the EDIT mode They can then be saved on disk or tape and re loaded later to be run again The program area can have any number of Color LOGO procedures in it Each procedure begins with a statement The statement must be the first and only statement on a line Other than that any number of statements can share a line each one is separated from the previous one by one or more spaces Each procedure should end with an END statement The work area may contain many procedures at once It is a good practice to leave at least one blank line between procedures to improve readability It is also suggested that program lines be indented to show the logical structure of the program The examples in this manual are all written in this manner TURTLE SPACE The TURTLE is a creature that has a visible SHAPE a POSITION and a HEADING The position is defined by an X Y coordinate pair The heading is defined by an angle from 0 to 359 In general the turtle lives on the plane of the display screen Using TURTLE GRAPHICS COMMANDS you can make the turtle move about and if desired leave a trail Initially a turtle starts at the HOME position The home position is the approximate middle of the screen X
91. n 1 the current line bumps down off the screen if not in column 1 then the current line is split at the cursor location into two lines SHIFT deletes the character under the cursor and moves the remainder of the line left to close the gap If the line has no characters then the blank line is removed SHIFT inserts a blank into the line at the cursor location by moving the remainder of the line right one space If the line is already full then no action takes place BREAK exits EDIT MODE and returns to BREAK MODE e allows the next character to be one of the specially marked single key command codes To enter a real O press twice In general to enter new lines just type each line followed by an ENTER press To modify a line move the cursor into place with the arrow keys then modify text by typing the new text over the old or by inserting or deleting characters as described above NOTE If the editor quits accepting new text then the program area is full The editor is general enough to be used not only for writing Color LOGO programs but for simple word processing applications After you edit a text file you may print or save it on disk or cassette for later use One such use would be writing documentation for modules written in Color LOGO Since the editor has a maximum line length of 32 characters a facility is provided to allow for printing of longer text lines on the printer If a line is ended with a
92. n adhesive tab use a small piece of opaque tape Insert the Color LOGO diskette in Drive the disk drive closest to the Color Computer on the cable Close the disk drive latch B AJ C K UP J 9 L T O 111 and press ENTER The computer will copy the contents of the diskette in Drive 0 onto the diskette in Drive 1 When the BACKUP process is complete you ll see the OK prompt reappear INDEX Note that the language summary in the Appendix begins on page 107 Therefore page numbers below 107 refer to discussions within the tutorial and page numbers above 107 refer to summaries in the language reference appendix BOR eate tots ate Sale fs 29 117 Addr sS s ron Sate es epp quaeque 91 Animation tL Stages ae 81 ARG ox d eet En nee duds 36 29 116 ASC 90 BACK nai ne ie us 10 114 BACKGROUND 31 114 BO ar Ta te 31 114 Binary tree wenn an se er 46 A A E 10 114 BREAK 4 24 dia tr be Eden 6 BREAK 6 107 120 CAU eiue Sn ae 114 Camera cus metus use 41 Cartridge usa de sealants 5 107 Cassette ai ini en em dal 5 39 Circle sudo AS 25 CBA Rcd nce es ED an 8 114 COLORSET 31 114 Complement 81 Communication 89 47 Control statement 72 Cur
93. n fix the procedure if we realize that what we are really drawing is a 36 sided polygon which looks like a circle because of the limited screen resolution The fix is the same as before start in the center of the side TO CIRCLE REPEAT 36 FD 3 RT 10 FD 3 END Now run PATTERN to verify that this set of procedures is a solution to the original problem 25 Let s analyze what we ve just done The road map for attacking the problem was to break the problem into a set of subproblems and in turn to break each subproblem into even simpler subproblems until the subproblems can be solved by a single REPEAT statement Specifically we broke the original problem into the problem of drawing SQUARE CIRCLE six times we broke SQUARE CIRCLE into the problems of drawing a square and drawing a circle These last two problems were easily solved with a single REPEAT statement In general we follow this sequence in attacking a problem although we do not insist that the lowest level procedure consist of a single REPEAT statement One of the reasons for using Color LOGO with children is that it is an excellent way to teach children a most powerful and useful general problem solving approach That approach is what we have just illustrated Basically it involves working from the overall view down to the details by breaking each problem into pieces 26 6 VARIABLES Variable is the name used to describe unique storage locations where numbers can be kept
94. n in BREAK mode that s the mode that you are in when you start You ve already been in RUN mode you got there from BREAK mode by pressing R Now we want to move into EDIT mode The map shows us that we need to leave RUN mode by pressing the key and then get into EDIT mode by pressing the E key EDIT mode provides what is called a line oriented editor EDIT mode is used to create and alter programs written in Color LOGO but for the rest of this chapter we will forget Color LOGO and concentrate on the mechanics of using EDIT mode We ll do something familiar write a note to Grandma Upon entering EDIT mode you ll see a short horizontal line appear at the start of the bottom line of the screen This line is called the cursor The cursor indicates where any typed letters numbers etc will appear Start the note by typing DEAR GRANDMA Press ENTER and the cursor moves to the start of the next line Type the next line as I M STARTING TO USE AN EDITOR Again press ENTER to complete the line Notice that this editor produces only upper case letters Color LOGO uses only upper case letters We could continue to enter as many lines as we wanted in the same fashion Let s assume that this is to be a very short note and that we now want to quit editing Press BREAK Upon reflection we decide to alter the note so we return to EDIT mode press E The first line of our note appears with the cursor at the start of th
95. ne of the current pen color is drawn as the turtle moves sets the background color of the screen to color 0 1 2 or 3 The default background color is 8 selects color set 0 or 1 For each set there are four distinct colors The default colorset is 0 paints the entire display area the background color and moves the current turtle to the home position moves the turtle forward the number of steps denoted by the value of the expression If the turtle s pen is down then a line of the current pen color is drawn as the turtle moves makes the turtle invisible sends the current turtle to position 128 96 with heading 0 LEFT expr PENCOLOR expr PENDOWN RIGHT expr SETHEADING expr SETX expr SETY expr SHAPE shape list SHOWTURTLE EXPRESSIONS LT PC PD RT SETH and SH SX SY ST turns the turtle left counter clockwise the specified number of degrees sets the pen color of the current turtle to color 1 2 or 3 The default color is 0 The actual color depends on the current color set If the pen color is set to the same color as the screen background color then the turtle pen will erase as it moves tells the current turtle to draw a line as it moves in response to FORWARD or BACK commands turns the turtle right clockwise the specified number of degrees points the turtle in the direction specified by the expres sion The heading can be from to 359 degrees 0 degrees is
96. nstead by renaming the procedures Ed ERR ADD As in DOODLE mode we want to have some way to erase mistakes The way to do this is to redraw the shape with the pencolor set to the background color We also have to pick a way for the child to control the erase One possibility is to use double presses of the same key to specify erase With a minor name change then we have the procedures TOT TO TT PC 1 PC 3 T1 T1 END END TO 1 SH 0 HT PD FD8 RT 150 FD 15 TRI 15 5 0 FD5 PU ST END The fact that we return the turtle to its original position makes this erase possible 59 Similar changes in Sand C give TOS TO 55 PC2 PC 3 51 51 END END TOC TO CC 0 PC 3 C1 C1 END END We have not bothered to reprint the original versions of C and S which must be renamed C1 and S1 While we are at it we should allow for double keystrokes of the DOODLE mode commands One example should be sufficient TO 77 PC3 BK 1 END We are in effect building a special language consisting of one keystroke commands Because of the low frustration tolerance of the audience that we are building the special language for it is especially important to make the language user proof To do that we should define a procedure for every other key on the keyboard The procedures are TOA TO B TO D END Note that we skipped C because it is actually used Note also that it is not necessary to have individual END statements for each procedure bec
97. nt as the process of seeking the goal Color LOGO is based on a set of ideas for use of the computer first developed under the name LOGO Many people have contributed to the LOGO project too many to list but we must mention the names Wallace Feurzeig Harold Abelson Andrea diSessa and with special emphasis Seymour Papert Most of the development and testing of LOGO was done at MIT There were two vital steps in bringing the LOGO approach to the attention of the educational community One was the publication of two books Mindstorms by Papert and Turtle Geometry by Abelson and diSessa Any serious user of LOGO will want to read those books The other was the implementation of the LOGO language on microcomputers a step which decisively moved LOGO from the laboratory into the classroom If you are already familiar with LOGO you will find much of Color LOGO to be familiar too Wherever possible we have kept the same syntax as LOGO and the logical structures of the two languages are essentially the same Most of the graphics programs in books on LOGO will run in Color LOGO without change Color LOGO is not just LOGO under another name for another computer there are some very important differences between the two Color LOGO is a graphics language but LOGO also includes a number of string operations drawn from the LISP language Color LOGO uses strings only as labels on graphics Color LOGO provides multiple turtles whereas most versions of LOGO
98. nter COLORSET 1 to change color set Then enter COLORSET 0 to change back Within each color set there are four colors numbered 0 1 2 and 3 The normal drawing color is color and the normal background color is color 8 Change the background color by entering BACKGROUND 1 or abbreviate BG 1 Change the pen or drawing color by entering PENCOLOR 2 or abbreviate 2 A portion of a drawing can be erased by setting the pen color to the same color as the background color is set and drawing over the unwanted part of the drawing Let s add color to some of our earlier procedures One interesting choice is FOUR Retype BOX see page 19 then enter the procedure FOUR as TO FOUR REPEAT 2 PC 1 BOX PC 2 BOX END and to allow easy experimentation make MANY into TO MANY N REPEAT N FOUR RT 90 N END 31 We would like to be able to name the colors you will get with specific pen colors and color sets but colors vary from TV to TV they vary with the color settings on the TV and they may even switch when you restart your computer Try running MANY with a value of 10 Then adjust the color and tint controls on your TV set to your satisfaction On many TV s color set 1 will give more interesting colors so be sure to try that too You can change color sets without redrawing the figure by typing COLORSET 1 An interesting variation can be created by the following changes TO BOX PC 1 FD 50 RT 90 PC 2 FD
99. o send mail or request location information about the turtle The main turtle is always number 0 Other turtles can have a number from 1 to 254 When a turtle other than the main one exists from the procedure given it when it was HATCHed it goes out of existence leaving behind only the lines it drew on the screen The VANISH statement also causes the turtle to go out of existence The main turtle in contrast can only go out of existence by executing a VANISH statement If the main turtle exits from the procedure given to it from RUN MODE it will return to RUN MODE where the user can then enter its next command or procedure to run If when the main turtle is in RUN MODE there are other turtles then the other turtles cease to move Each time the ENTER key is pressed each of the turtles executes one program statement This has the effect of stepping the hatched turtles along at a controlled pace A useful debugging method is to HATCH a turtle from RUN MODE and tell it to run the procedure which is to be tested Then the procedure is run by pressing ENTER repeatedly If you enter a VANISH command then the main turtle will disappear and the hatched turtle will run at full speed 119 ERROR MESSAGES FROM COLOR LOGO In BREAK MODE a is displayed if any key other than a valid command letter is pressed A load or save command may also display a digit followed by a 1 2 3 4 6 memory
100. of one unit the only angles which were possible were 45 degrees apart 0 45 90 In DOODLE mode the only steps forward possible are one unit and ten units We ve already said that the only turns that make any difference with one unit forward are turns which are multiples of 45 degrees The only turns which make sense with ten units forward are multiples of 15 degrees This is not as obvious or as absolute as the one unit forward case so if you don t see the problem try the following procedure TO TEST ANGLE RT90 ANGLE REPEAT 2 FD 10 END The design decision was that 15 degrees was the smallest divisor of 45 degrees that gave a smooth line at an angle If you want to make a line at some other angle in DOODLE mode you can It just requires more keystrokes The combination of FD 1 operations and either no turn or a turn of 45 degrees will allow the drawing of a line at any angle For example a very small angle could be drawn by repeating the series FD10 key 8 followed by nine FD 1 s key 7 an RT 45 key 5 an FD 1 and an LT 45 key 6 the desired number of times This sounds awkward but remember that it will be necessary very seldom Most young children will find sufficient accuracy with turns of 15 and 45 degrees DOODLE Mode characters are not available on printers If you try to print a procedure created in DOODLE mode the special characters will appear as lower case letters Thus it is impractical to print DOO
101. ok exactly like the final turtle for several reasons Lines drawn in DOODLE mode are two dots wide but lines drawn as turtle shapes are one dot wide Also lines which cross complement when they are parts of turtle shapes but they do not complement in DOODLE mode However you will get to see the shape in about the final form and of exactly the final size while drawing it Once you have the shape completed in DOODLE mode you can enter EDIT mode and convert the procedure into one to draw a new shape Simply insert the SHAPE command before the command list and convert each 3 to U each 4 to D each 5 to R each 6 to L and each 7 to F all by overtyping Let s begin with a very simple example We want the turtle to appear as an arrow On graph paper we draw the dot pattern x Rx X The actual turtle position is to be at the tail end of the arrows Enter DOODLE mode naming the procedure NEW and draw the figure The keystrokes are 777777766677555537755747 You may be surprised at the small size of the turtle but you can always draw a new one after you ve learned the technique Now enter EDIT mode and look at NEW Insert SHAPE before the list of 82 symbols and replace the DOODLE symbols with the appropriate turtle shape commands Don t forget to include the hyphen at the end of the first line of commands At this point your procedure should be TO NEW SHAPE FFFFFFFLLLFFRRRR UFFRRFDF END To see how your shape looks run NEW and th
102. overtyping replaces characters We need to delete the remaining letters which we do by holding down the SHIFT key and pressing the left arrow key We can see the rest of the lines in the procedure by pressing either ENTER or the up arrow key 4 several times 18 It is good programming practice to clarify the structure of a procedure by indentation Here we want the procedure BOX to look like this TO BOX FD 50 RT 90 FD 30 RT 90 FD 50 RT 90 FD 30 END To make these changes we must insert a couple spaces at the beginnings of the second and third lines Move the second line to the bottom of the screen by using the up and down arrow keys The cursor will move to the start of the line whenever you change lines To insert spaces hold down the SHIFT key and press the right arrow key If this does not insert spaces it means that the line is already full Insert spaces at the start of line 3 as well The structure of the procedure would be even clearer if it were typed as follows TO BOX 50 RT 90 FD 30 RT 90 FD 50 RT 90 FD 30 END These changes require us to break single lines into multiple lines To break a line position the cursor where you want to break the line hold the SHIFT key down and press the down arrow key What if we want to add lines to a procedure for example if we want to add a diagonal line through the box We ll have to tell the turtle to turn and go forward You d better run
103. p between levels 1 and 2 are controlled by the REPEAT 4 statement in FOUR down to level 2 four times and the END statement in BOX up to level 1 44 In a program like POLYSPI the path is actually less complex Level O POLYSPI Level POLYSPI Level 2 POLYSPI Level 3 POLYSPI The transitions down are controlled by the statement POLYSPI SIZE STEP ANGLE STEP There are no transitions back up because the procedure never reaches the END statement Thus the computer sinks down level after level until it finally runs out of memory POLYSPI gives interesting figures because of the difference in the values of the variables at the different levels We begin the program with the command POLYSPI 1 90 5 Level 0 The recursive call of the procedure is when we substitute the current values of the variables POLYSPI 6 90 5 Level 1 Therefore at level the FD command is for length 1 and at level 1 the FD command is for length 6 The pattern continues POLYSPI 11 90 5 Level 2 POLYSPI 16 90 5 Level 3 until the turtle runs off the screen NOWRAP or the computer runs out of memory WRAP Another procedure of this type is called INSPI In INSPI the angle is incremented recursively TO INSPI SIZE ANGLE STEP FD SIZE RT ANGLE INSPI SIZE ANGLE STEP STEP END Again this is one to play with Try INSPI 10 90 5 INSPI 10 90 3 INSPI 7 5 3 do SX 80 SY 140 first to get it all on the screen INSPI 3 5
104. provide only a single turtle Color LOGO thus can be used to introduce important concepts like multi programming and messages via mail boxes but still with great simplicity Consequences of multiple turtles include provision for simple animation and the potential for user created games All these are possible because in contrast to LOGO the memory requirements of Color LOGO are modest Color LOGO also provides a mode for doodling designed for children who are too young to type keywords reliably If you are just starting on computers all that sounds rather complex That s because we re just talking about it instead of doing it Let s do it 2 GETTING STARTED There are two ways you can start Color LOGO running on your TRS 80 Color Computer from a plug in cartridge or from disk You will want to have some way to store your favorite creations for future display so you will want to have either a disk drive or a cassette player attached to your computer system Consult the chapters on Installation and Operation in your copy of the TRS 80 Color Computer Operation Manual for instructions as to proper cable connections for the disk and or the cassette player DO NOT TURN ON THE POWER YET NOTE If you have the ROM version of Color LOGO Cat No 26 2722 follow the steps under Plug In ROM Cartridge Then turn the page to Using the Color LOGO Program For the disk version Cat No 26 2721 follow the steps under Dis
105. r left turn Now let s make the turtle move backwards Try BACK 40 or in abbreviated form BK 40 Notice that the turtle is somewhat transparent You can see the track through the turtle If you d rather not see the turtle at all you can hide it Enter HIDETURTLE 10 Here the abbreviation HT is much shorter The turtle is still there but invisible Enter LT 30 BK 30 to see the invisible turtle s track To make the turtle visible again type SHOWTURTLE you guessed it abbreviated ST and to turn it away from the track type LT 120 At this point the only thing between us and an endless variety of stunning graphics is an immense amount of typing To learn how to minimize the typing we have to learn how to create and use procedures 11 3 MODES AND EDITING New users of computers often find the idea of modes awkward Mode is the term used to describe the separation of the various things a computer language can do into groups There are a number of good reasons for having various modes One is that there are not enough different keys on the keyboard to control all the different things that need to be done The same keys can be used for different tasks in different modes without confusion at least on the computer s part The following diagram is a map of the modes in Color LOGO KEN BREAK 2525 EDIT DOODLE The keys which trigger the jumps between modes are indicated on the arrows You ve already bee
106. r LOGO package can be used with a ROM based TRS 80 Color Computer with Color BASIC and with at least 16K of memory Procedures that you write ean be saved on cassette tape 1 A BIT ABOUT COLOR LOGO Color LOGO is a computer language for children Like all the best things for children Color LOGO can provide endless fascination and challenge for adults as well At first glance Color LOGO may seem to be simply a language for drawing pictures since the result of running a Color LOGO program is almost always a picture However Color LOGO is far more than an easy way to draw pictures Color LOGO is a tool for learning about some of the most powerful concepts in mathematics physical sciences computer science and problem solving but in a way so appealing and simple that even a kid can do it Notice that we said that Color LOGO is a language for learning we very intentionally did not say that Color LOGO is a language for teaching The role of the learner is all important Color LOGO puts the student in the role of explorer one who sets goals problems to solve and tries to find a way to those goals The role of the teacher is guide one who stays in the background as much as possible one who does not set the goals for the learner and one who only assists when asked Effective use of Color LOGO has much of the flavor of play It s not whether you win or lose but how you play the game The goal the student reaches is not as importa
107. recognize which key has been depressed and to send a message to the appropriate turtle We have to decide what keys to use for what actions of the runner and the chaser We decided on the following key assignments S move runner forward A turn runner left D turn runner right move chaser forward J turn chaser left L turn chaser right So now we see what if any key was pressed First look at the statement IF X 5 SEND 2 1 90 The literal S gives the ASCII value of the argument S That is the condition X combination with the previous KEY function checks to see whether the S key was depressed If the S key was depressed then the statement SEND is run The SEND statement sends a message to another turtle by leaving the message in a mailbox The first number after the SEND is the address of the message In the line we are analyzing the address is 2 so this message can be picked up from the mailbox only by turtle 2 The address can be an expression as well as a number The second number after the SEND is the message Here the message is the number 1 in general the message can be any number in the range covered by Color LOGO 32768 to 32767 or an expression which gives a number in this range To review SEND 21 leaves the message 1 in the mailbox for turtle 2 Because the S key is to move the runner turtle 2 the message 1 must mean move We ll see that in the procedure RUNNER Although we aren
108. red part then draw the blue part We can put delays between the strokes to make the sequence on the example visible We ll use both techniques 66 TO DRAW F CLEAR SX 50 SY 146 RT 180 PC 1 FD 50 WAIT 6 SX 50 SY 146 LT 90 PC 2 FD 30 WAIT 6 SX 50 SY 126 FD 20 WAIT 6 HOME END TO WAIT T REPEAT T REPEAT 820 END Notice that the procedure WAIT does nothing but count The number on the inner REPEAT is picked so that the number T is approximately the number of seconds that are used up counting Be sure that the child s procedure is named F so that there is a simple correspondence between the name and the drawing If you still have the OK Set in memory you ll have to delete F from that set Once the child is familiar with the shape of the letter or of several letters you can let them try making letters by connecting dots Here the procedure must draw the dots preferably starting at the home position TO DOTM CLEAR DOT FD 60 DOT RT 135 FD 30 LT 45 DOT LT 45 FD 30 RT 45 DOT RT 90 FD 60 DOT HOME END 67 In this procedure we ve been careful to always have the turtle pointing in the horizontal direction to keep the spacing of the dots perfectly regular That may not be essential This dot to dot exercise works best for those letters and numbers where the pen never need be raised Most letters require that the pen be raised The dot pattern for these may be a bit of a puzzle perhaps a worthwhile challenge If that is too
109. riables When you run it you may get less than you expected Why does the program stop before drawing the boxes Notice that there are four turtles on the screen the three you created with the HATCH commands and as always the master turtle When there are multiple turtles Color LOGO gives each turtle a turn in sequence A turn is a single turtle command or a logical operation in a control statement A control statement is a statement which controls the sequence of operations in the procedure for example IF or REPEAT Therefore having created turtle 1 Color LOGO gives turtle 1 a turn and creates turtle 2 then it gives turtles 1 and 2 each a turn and creates turtle 3 Next it gives turtles 1 2 and 3 each a turn and encounters the END instruction Because turtle 0 is always there turtle 0 is now waiting to find out what to do We have not given turtle anything else to do so it is waiting for a command from the keyboard If we press a command for turtle 0 to do nothing then all the other turtles get another turn Try it Remember this as a way to single step through procedures to find errors Of course we do not always want to have to sit at the keyboard pressing ENTER We can get the whole thing to work as planned if we give turtle some procedure to run as well Try TO TEST HATCH 1 BOX 50 30 60 HATCH 2 BOX 40 180 40 HATCH 3 BOX 60 100 20 BOX 20 150 120 END The last call of BOX has no HATCH preceding
110. rocedure name can be almost anything the computer assumes that any characters which don t form a correct keyword must form a procedure name If the characters are really a typing error then the name is not found in the list of procedures and the error message is sent Next type in the turtle commands for drawing the rectangle That is type FD 50 RT 90 FD 30 RT 90 FD 50 RT 90 FD 30 Many commands can be typed on a single line as long as they are separated by one or more spaces To finish the procedure type END on a new line and press ENTER 17 To try out RECTANGLE you must leave EDIT mode by pressing the BREAK key and get into the RUN mode by pressing the R key To actually run the procedure enter RECTANGLE That s so neat that we should try it again and again Type and enter the procedure name at least three more times Now the screen should show By placing procedure RECTANGLE in the computer s memory we have taught the turtle to understand a new word The turtle now understands RECTANGLE in the same way that it understands LEFT RIGHT FORWARD and BACK Before moving on to other procedures we want to review use of the editor Press to return to BREAK mode and press E to reenter EDIT mode The screen should now show the first line of the procedure RECTANGLE Let s change the name to BOX Use the right arrow key DJ to position the cursor under the R in RECTANGLE Then type BOX Remember
111. rocedures in memory will be printed If for some reason you want to eliminate the line feed at the end of any line thus using a larger portion of the paper width get into EDIT mode and insert an character at the end of every line for which you want to eliminate the carriage return and line feed To place an character in a line in EDIT mode you ll need to press the 8 key twice There remains the question of saving results the pictures on the screen We find that the best way is to take pictures this is the only way to get color at any reasonable price To avoid false patterns due to interactions of the camera shutter with the video display we recommend a shutter speed of 1 2 second Use a tripod and a cable release for the camera The lens setting is somewhat dependent on the brightness setting of the TV and of course on the film speed A good starting point is to set medium brightness on the TV and use a lens opening of about f8 with film speed of 100 ASA The reds are likely to come out rather brownish and commercial developers are likely to overexpose prints with large dark backgrounds However the illustrations in this manual are typical of what can be done without much trouble You will minimize distortion if you use a telephoto lens This chapter is short because there is very little complication in saving loading and printing programs Remember that you have a very large procedure space available so if you are starting a new
112. s been opened or if the Equipment or Software has been subjected to improper or abnormal use If a manufacturing defect is discovered during the stated warranty period the defective Equipment must be returned to a Radio Shack Computer Center a Radio Shack retail store participating Radio Shack franchisee or Radio Shack dealer for repair along with a copy of the sales document or lease agreement The original CUSTOMER s sole and exclusive remedy in the event of a defect is limited to the correction of the defect by repair replacement or refund of the purchase price at RADIO SHACK S election and sole expense RADIO SHACK has no obligation to replace or repair expendable items B RADIO SHACK makes no warranty as to the design capability capacity or suitability for use of the Software except as provided in this paragraph Software is licensed on an AS IS basis without warranty The original CUSTOMER S exclusive remedy in the event of a Software manufacturing defect is its repair or replacement within thirty 30 calendar days of the date of the Radio Shack sales document received upon license of the Software The defective Software shall be returned to a Radio Shack Computer Center a Radio Shack retail store participating Radio Shack franchisee or Radio Shack dealer along with the sales document Except as provided herein no employee agent franchisee dealer or other person is authorized to give any warranties of any nature on behalf of
113. sed then the value is the ASCII value of the character returns the absolute positive value of the argument returns a random number from 0 to arg 1 returns the X coordinate of the turtle with the specified identification note XLOC gives your own X coor dinate If no turtle exists with the identification then 128 is returned returns the Y coordinate of the turtle with the specified identification note YLOC ME gives your own Y coor dinate If no turtle exists with the identification then 92 is returned returns the heading 0 to 359 of the turtle with the specified identification note HEADING ME gives your own direction If no turtle exists with the identification then 0 is returned returns a measure of the distance from the current turtle to the one with the specified identification The measure is equal to the number of steps in the X direction plus the number of steps in the Y direction If no turtle exists with the specified identification then the distance to HOME is measured returns a number value MAIL is used to check for and receive messages sent via the SEND command The argument of the MAIL function denotes the source from which messages are to be received If the argument is 255 then mail is received from any turtle that has sent mail addressed to the current turtle If the argument is not 255 then it denotes the identification of the turtle from which mail is to be received
114. sors votati osse dle ee he TRUE RN 13 Delete nales calcita a 2 4 14 109 Directory enden Leva ot 39 Diskette ce ee eR Rh 5 39 107 DOODLE mode 53 111 DSKINI 39 123 124 Edit 54 EDIT 13 108 Editors essen 13 108 ELSE een 76 112 END et 113 End loop recursion 43 HAS Ch its dee tees daiwa ea er 31 Erase DOODLE 59 Error message 120 Expression 29 112 ED ce Anat 7 114 Format e UR d 39 FORWARD iex gs 6 114 Ertact al ic ici wee petu iud 49 Functions 117 Game controller 93 Games did 89 Global variable 28 116 FAT GUS a 71 113 Heading isos cea vee RR Ro her E 35 HEADING ok haces bin 117 HIDETURTLE 10 114 HOME enh tea De ee ex A 35 114 Home position 85 FIT sed ou teed De RR oon Reka dx 10 114 TPs ER Medea Rake a Dee an 47 112 Indentation mitico coto ee dete 19 Insert se talk Be ees ck ie 14 15 109 KEY ren al 90 117 Keyword 2 14 gna ele ine eres ewe end 17 LEFT 23 Se tats sagen 10 115 TOV EL sce esd Gath eo a tht ne 44 AGES Ps Pm 3 literal str ata el Lr Dr a oes T 91 116 POAC tins feo ats os as BOR T 5 39 107 Local variable
115. straight up moves the turtle by changing its X coordinate to the value specified No line is drawn The value may be from 0 left edge to 255 right edge moves the turtle by changing the Y coordinate to the value specified No line is drawn The value may be from 0 bottom to 191 top changes the shape of the current turtle to a shape denoted by the shape list See TURTLE SHAPE LIST below makes the turtle visible The expr designation above denotes a place in which an expression can be substituted An expression can be a number a variable a function reference or a combination of these and the operators shown below An expression is always evaluated to a number from 32768 to 32767 Expressions may contain parentheses and are in general evaluated in the same manner as those in BASIC or other languages 115 ARITHMETIC OPERATORS These operators result in a number from 32768 to 32767 addition subtraction multiplication division LOGICAL AND RELATIONAL OPERATORS These operators always result in a 1 for TRUE or a 0 for FALSE amp logical AND logical OR NOT logical negation lt less than 2 greater than equal to lt gt not equal to lt less than or equal to gt greater than or equal to VARIABLES A variable consists of a colon followed by a word containing any number of letters or numbers A variable represents a unique storage location for a number If a variable is given on a TO stat
116. t a similar chance to enter FORWARD 40 You can use the left arrow key to correct typing errors before you press Simply backspace to the beginning of the error and retype the turtle instruction Now I want you to find out how far it is from the center of the screen to the top To get a fresh start and a clear screen enter the word not the single key CLEAR Then try to make the turtle track go to the top of the screen with a single FD command When you have it exactly right the turtle itself will wrap around appearing at the bottom of the screen but the line will be drawn to the top of the screen No doubt it will take you several tries of CLEAR FD to hit the top exactly By now you re probably tired of drawing vertical lines It s time to turn the turtle Clear the screen CLEAR ENTER and enter FORWARD 40 RIGHT 90 To make the change more obvious enter FORWARD 59 1 oe The turtle understands degrees If you are using Color LOGO with small children we have a suggestion There is now quite a bit of information gathered about effective use of LOGO with small children and that information applies to the use of Color LOGO as well Color LOGO is a language for experimentation not a language to learn by imitation of items from a textbook Resist any temptation to explain degrees to the child who does not already know about them The child will learn about degrees easily from
117. t same shape At one additional level of detail that gives Each of the lines in this drawing is in turn made up of four lines with the basic shape etc This is a place to use recursion TO FRACTAL N IF N lt 15 FD N STOP FRACTAL N 3 LT 60 FRACTAL N 3 RT 120 FRACTAL N 3 LT 60 FRACTAL N 3 END FRACTAL ee A Running FRACTAL 59 will show the pattern You may want to enter RT 90 and SX 0 before running FRACTAL 50 to turn it the way we ve drawn it in the manual Notice that the pattern divides the whole length into thirds that is why we divide by 3 on the recursive calls However the resulting length will change somewhat depending on the conditional IF statement because of the roundoff loss in integer arithmetic You ll see that if you change the conditional to something finer say N lt 4 That pattern looks like the edge of a snowflake Why not make it into something six sided 49 TO FLAKE N CLEAR REPEAT 6 FRACTAL N RT 69 END You may have to play with the starting position SX and SY and the size to get a nice figure without wrap around You may also prefer the figure you get when FLAKE is made to draw three sides at 120 degrees D gt E 2 LAR Other variations are possible We can replace FD N in the IF statement with a more elaborate series of commands A few examples follow TO FLAKE N CLEAR SX 50 SY 50 REPEAT 3 FRACTAL N RT 120 END Replace the cond
118. the various keys If the children are very young this will take quite a bit of time If you ve changed the shapes available in the OK Set since the last session then you should give the child another chance to explore the new set of keys Keep in mind that a child s attention span is not as long as yours so don t try to prolong the sessions Our own first ideas for Color LOGO grew from an effort to create something for a four year old to do because he wanted to be like Dad and work on the computer This suggests that another way to start is to master DOODLE mode yourself and to prepare a set of procedures for the OK Set Then you ll be ready when an interested face appears at your shoulder some evening The users of LOGO have had consistent success with one technique for getting children started They repeatedly relate the turtle commands with body movement That is ask the child to play turtle and ask them to keep track of the turtle movements they make Thus if the task is to draw a box the child is asked to walk in a box shaped path and then to tell the turtle what he or she did The success on which this recommendation is based comes from work with somewhat older children so it may not be quite as effective with the pre reading group It might help to give them objects to actually walk around to make the shape less abstract One heavily used technique in early childhood teaching is to ask the student to copy something A book titled
119. tion to detail can make the exercises much more effective Especially with very young children be sure to try out the task to check the difficulty level before they are around This is supposed to be fun as well as instructive and not a new source of frustration The same pieces can be used for a slightly more difficult exercise TO PATTERN2 DOTS SX5 SY 150 REPEAT 6 PD LT 60 FD 40 RT 120 FD 40 LT 60 SX 5 SY 55 LT 90 FD 10 RT 90 FD 40 RT 90 FD 10 BK 10 LT 90 END 63 Here the task is to reproduce the indicated pattern by continuing the shapes started on the lower line Because the two shapes forming the pattern are different the focus is on the shape rather than straight copying We may as well make use of some of the fancier shapes that we have defined in the OK Set The following is another example of complete the pattern but one which is visually more interesting TO PATTERN3 MAKE X 0 MAKE Y 50 CLEAR HT REPEAT 19 REPEAT 7 SX X SY Y SQUARE Y 20 MAKE X X 20 MAKE Y 50 MAKE X 11 MAKE Y 58 REPEAT 4 REPEAT 5 SX X SY Y T MAKE X X 40 MAKE X 11 MAKE Y Y 40 SX 31 SY 158 ST END TO SQUARE REPEAT 4 FD 20 RT 90 END The child s task is to complete the pattern by moving the turtle and by pressing the key with the triangle Many other variations on this theme are possible The PATTERN3 procedure makes heavy use of the MAKE statement and we have not d
120. tion arising out of any claimed breach of this Warranty or transactions under this Warranty may be brought more than two 2 years after the cause of action has accrued or more than four 4 years after the date of the Radio Shack sales document for the Equipment or Software whichever first occurs D Some states do not allow the limitation or exclusion of incidental or consequential damages so the above limitation s or exclusion s may not apply to CUSTOMER NCLUDING WARRANTIES OF IV RADIO SHACK SOFTWARE LICENSE RADIO SHACK grants to CUSTOMER a non exclusive paid up license to use the RADIO SHACK Software on one computer subject to the following provisions A Except as otherwise provided in this Software License applicable copyright laws shall apply to the Software B Title to the medium on which the Software is recorded cassette and or diskette or stored ROM is transferred to CUSTOMER but not title to the Software C CUSTOMER may use Software on one host computer and access that Software through one or more terminals if the Software permits this function D CUSTOMER shall not use make manufacture or reproduce copies of Software except for use on one computer and as is specifically provided in this Software License Customer is expressly prohibited from disassembling the Software E CUSTOMER is permitted to make additional copies of the Software only for backup or archival purposes or if additional copies are required
121. tions As is our custom we will illustrate with an example We want to use the following stick figure as a turtle shape XXX X XXX We must choose our pathway through the figure carefully The problem points are points where lines meet To avoid problems we avoid shortcuts and return to junction points by backtracking exactly The pathway we take is indicated on the second figure The dotted lines indicate backtracking with the pen raised Remember if we did not raise the pen when backtracking then the lines would be complemented a second time that is erased The only place where we don t backtrack is on the head If a closed figure is symmetric then it will stay closed when rotated The other point to note carefully is when to raise and lower the pen A dot will be complemented if the pen is down when we move into the dot or if the pen is lowered while we are in the dot Notice that this means that if we draw a line and then cross that line with the pen down the crossing dot will be erased Following the pathway indicated gives the following procedure As stated earlier we would work this out on paper and enter it directly in EDIT mode so that we could use the B command TO ONE SHAPE LLULLFFFFDFFRRRFFFFFF RRFFFFFFLLFFUBBLLFFFFFFRFD FFFFFFFFRRFFFFLFFUB BRBBBB RFDFFFLLFFUBBLLFFFFRFD FFLFRFFRFRFFRFRFFRFRF END Try this out by running ONE Try rotating it to other positions Notice that when you turn it far enough it is upsid
122. to read the manual so a parent or teacher will have to assist them in learning In this and the next chapter we will teach the assistant the mechanics of two ways to use Color LOGO with children actual suggestions for activities with the children are gathered together in Chapter 13 In this chapter we will cover the mechanics of DOODLE mode The idea of DOODLE mode is that a minimum set of turtle commands can be entered by single keystrokes from the keyboard Before proceeding you should get the plastic overlay for the keyboard which was supplied with the Color LOGO package This overlay fits over the top row of the keyboard The symbols on the overlay show the meanings of the numeric keys in DOODLE mode see Appendix 1 page 107 These symbols will appear at the bottom of the screen in DOODLE mode when the keys are pressed and they will appear in the procedures that you create in DOODLE mode DOODLE mode is entered from RUN mode by pressing the 9 key When the O key is pressed an appears at the bottom of the screen This is the indication that it is time to name the procedure you are creating Simply type the name you want to use the name can be as simple as a single letter or number After typing the name press ENTER The computer is now in DOODLE mode and the top row of keys has its new meaning The meanings of the keys are 1 CLEAR 2 HOME 3 PENUP 4 PENDOWN b RT 45 6 LT 45 7 FD 1 8 FD 10 9 RT 15 0 LT
123. ures in memory Let s first learn how to save on tape Of course the tape recorder must be plugged in as described in the Operation Manual for the TRS 80 Color Computer Make sure that the volume control is set close to 5 Rewind the tape REWIND STOP Next press the RECORD and PLAY buttons down together If you are not using leaderless tape pull out the MIC plug for about 5 seconds This will make sure that you begin recording on blank tape Now you are ready to record the procedures Simply respond T ENTER to the SAVE prompt LOGO SAVE T When the recording is done the BREAK mode prompt will be displayed again If a number and a question mark appear after the T then the procedures were not saved properly so try again Disks must be formatted before use with Color LOGO Disks can be formatted using the DSKINI command when the computer is running BASIC However Color LOGO does not use the BASIC directory so once a disk is used for storing Color LOGO programs it must not be used with BASIC programs If you do not have a formatted disk save your procedures on tape as described above and turn off the Color Computer Then turn the computer back on The computer will be running BASIC now Insert a blank disk remember label towards the latch Then type DSKINIO and press ENTER If you get an error message remove the disk center itin its paper wrapper and try again Because it is always a good idea to keep duplicat
124. ures they create in DOODLE mode they can make their own key labels and attach them as they name the procedures For example you could suggest that they draw a truck a house a tree and a person in DOODLE mode and then let them draw street scenes using these additions to the OK Set Of course they ll soon want to add color To do that they ll have to learn how to insert PC commands into their procedures and before long they ll be typing and editing in the standard way 69 14 MULTIPLE TURTLES So far we have been drawing on the screen with a single turtle Complex figures were made by drawing one piece at a time first one piece completely then a second piece etc until the drawing was complete In Color LOGO there is another way to produce a complex drawing We can draw all the parts at once using several turtles Multiple turtles provide many extra possibilities Games are one obvious application It is much easier to program games if each player is assigned a turtle which maintains its position until that player s next turn This is especially true in Color LOGO as we often do not know the position of the turtle in absolute coordinates in which case it is hard to store a return point We shall see that it is often possible to simplify the programming by giving individual turtles different subtasks in a game We can make drawings by assigning turtles to the tasks of drawing individual pieces of the whole In this way the drawing wi
125. urtle that requests its mail Any other value denotes that the message can be received only by a turtle with the specified identifica tion see also the MAIL function The value of the sec ond expression is the value sent to the other turtle 113 procname arglist SLOW expr TURTLE GRAPHICS COMMANDS Statement Abbreviation BACK expr BK BACKGROUND expr BG COLORSET expr CLEAR FORWARD expr FD HIDETURTLE HT HOME 114 This is referred to as a CALL statement even though it does not contain the word CALL To CALL any pro cedure just enter its name followed by any arguments to be passed If arguments are present they are separated by one or more spaces Each argument may be a num ber a variable a function reference or an expression contained in parentheses The argument s values are passed to the parameter variables on the TO statement of the called procedure If there are fewer arguments than there are parameters on the TO then extra parameters are set to 0 If the called procedure executes a STOP or END then control continues with the next statement after the call statement The SLOW statement causes execution to slow down so that it can be watched more closely The value of the ex pression denotes how slow to go A value of 127 is the slowest speed A value of is full speed Meaning moves the turtle backward the number of steps denoted by the value of the expression If the turtle s pen is down then a li
126. ype of recursion The following program appears in all LOGO books and manuals TO POLYSPI SIZE ANGLE STEP FD SIZE RT ANGLE POLYSPI SIZE STEP ANGLE STEP END This procedure is so much fun to play with that I think you should do so before we get involved in any explanations One suggestion before you start the figures created are likely to outgrow the screen long before the memory runs out The wrap around feature of the screen will then lead to some striking but puzzling effects To start with let s prevent wrap around Enter RUN mode and type NOWRAP 43 Then try a variety of runs for example POLYSPI 1 90 1 POLYSPI 1 90 5 POLYSPI 1 120 3 POLYSPI 1 122 3 POLYSPI 1 144 5 POLYSPI 1 145 1 POLYSPI 1 176 3 mitra de A Na If you then want to see what happens when the computer allows wrap around type WRAP and try some more runs Now let s try to figure out what is going on with this POLYSPI It is useful to think of a Color LOGO program in terms of levels the main program is a procedure at level 0 a subprocedure called from level 0 is at level 1 a subprocedure called from level 1 is at level 2 etc The operation of a program like MANY can be diagrammed as Level O MANY Level FOUR Level 2 BOX The transitions down and up between levels 0 and 1 are controlled by the REPEAT statement in MANY down to level 1 and the END statement in FOUR up to level 0 The transitions down and u

Color Logo / Cat. No. 26-2722 / Year: 1982 - TRS

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