XLOGO User Manual
Contents
1. SC w word l list A good example to explain this save test lgo proc1 proc2 proc3 saves in the file test lgo in the current directory the procedues procl proc2 et proc3 If the extension lgo is omitted it is added by default The specified word gives a relative path starting from the current directory This command will not work with an absolute path changedirectory cd e w word Opens and reads the file w For example to delete all the defined procedures and load the file test lgo you would use efns load test Leo The specified word gives a relative path starting from the current di rectory This command will not work with an absolute path Saved w word saved test lgo saves in the file test lgo in the cur rent directory the collection of procedures currently defined If the extension lgo is omitted it is added by default The specified word gives a relative path starting from the current directory This command will not work with an absolute path id file When you want to read or write in a file you must openflow first open a flow toward this file The argument file must be the name of the file you want You must use a phrase to show the name of the file in the current directory The id argument is the number given to this flux so as to identify it 25 ETE f none Shows the list of the various open fluxes with their listflow identifiers id Opens the flow which identifier corresponds to the r2. integer Returns true if a is a list false otherwise list Returns true if a is an empty word or an empty list seat equal ab words Returns true if a is before b in terms of alphabetical ab If b is a list specifies if a is an element of b If b is a word specifies if a is a letter in b If b is a list look for the element a in this list There are two possible outcomes If a is in b returns a sublist containing all list ele ments from the first instance of a in b If a is not in b returns the word false If b is a word look for the character a in this word There are two possibilities If a is in b return the latter part of the word starting from a Otherwise return the word false member o cocoa return ocoa member 3 1 2 3 4 returns 3 4 anything Returns the word true is the pen is down false other pd pendown wise anything Returns the word true if the turtle is visible false oth visible erwise a word Returns true if the word is an XLOGO primitive false otherwise member prim primitive a word Returns true if the word is a procedure defined by the user false otherwise proc procedure 21 4 6 Testing an expression with the primitive if As in all programming language Logo allows you to check if a condition is satisfied and then to execute the desired code if it s true or false With the primitive if you can realize those tests Here is the syntax if expr
3. writelineflow 2 abcdefghijklmnopqrstuvwxyz writelineflow 2 abcdefghijklmnopqrstuvwxyz writelineflow 2 0123456789 You close the flux to end the writing closeflow 2 Now you can see the writing procedure went alright You open a flow towards the file you want to read This flow is given the number 0 openflow 0 c example You read the one after the other the different lines from the file pr readlineflow 0 pr readlineflow 0 26 pr readlineflow 0 You close the flow closeflow 0 if you wish to add the line Great setdirectory c openflow 1 example appendlineflow 1 Great closeflow 1 27 4 9 Advanced fill function Two primitives allow to colour a figure The primitive fill and fillzone These primitives allow a shape to be coloured in These primitives can be compared with the fill feature available in many image retouching programs This feature can extend to the margins of the design area There are two rules that must be adhered to in order to use this primitive correctly 1 The pen must be lowered pd 2 The turtle must not be located on a pixel of the colour with which the shape is to be filled If you want to colour things red it can t be sitting on red Let s take a look at an example to see the difference between fi11 and fillzone The pixel under the turtle is white right now The primitive fill will colour all the neighbouring Figure 4 1 At the beginning white
4. 15 sequence seq 31 setcolortext sct 16 setdirectory setdir 25 setfontname set n 15 setfontnametext setfnt 16 setfontsize setfs 15 setfonttext sft 16 setheading 13 setindexsequence sindseq 31 setinstrument sinstr 31 setitem replace 19 setpencolor setpc 14 setpenwidth setpw 14 setpos 12 setscreencolor setsc 14 setseparation setsep 15 setshape 14 setstyle ssty 16 setturtle sturtle 31 setx 12 setxy 12 56 sety 12 shape 15 showturtle st 13 sine sin 17 sqrt 17 stop 30 stopall 30 sty style 16 sum 17 tangent tan 17 thing 24 time 39 to 22 towards 14 trace 23 true 21 turtle 31 turtles 31 unicode 20 visible 21 wait 39 wash 13 while 34 white 11 window 14 word 19 word 21 wrap 14 write 16 writelineflow 26 yellow 11 zonesize 15 57
5. 24 erase er 24 executetcp 40 false 21 fill 28 fillzone 28 findcolor fc 14 first 19 fontname 15 fontnametext fnt 16 fontsize 15 fonttext ftext 16 for 33 forward fd 12 fput 19 gray 11 green 11 heading 14 hideturtle ht 13 home 12 if 22 indexsequence indseq 31 instrument instr 31 integer 17 integer 21 item 19 key 35 kill 24 killturtle 31 label 13 labellength 13 last 19 left lt 12 lighteray 11 list 19 list 21 listentcp 40 listfiles list 25 listflow 26 listvariables lvars 24 load 25 loadimage li 25 local 24 localmake 24 log10 17 Iput 19 magenta 11 make 24 member 21 member 21 message msg 15 minus 17 mouse 36 not 18 number 21 openflow 25 or 18 orange 11 output op 30 pasttime 39 pencolor pc 14 pendown pd 13 pendown pd 21 penerase pe 13 penpaint ppt 13 penreverse px 13 penup pu 13 pi 17 pick 19 pink 11 play 31 poall 24 pos 14 posmouse 36 power 17 pr print 16 primitive prim 21 print pr 16 procedure proc 21 product 17 purple 11 quotient 17 random ran 17 read 35 readchar 35 readcharflow 26 readlineflow 26 readmouse 36 red 11 remainder 17 remove 19 repaint 14 repcount 33 repeat 33 reverse 19 right rt 12 round rnd 17 run 24 save 25 saved 25 screencolor sc 14 sendtcp 41 sentence se 19 separation sep
6. word ez pr se elles word word ont end Fr_future parler je parlerai tu parleras il parlera nous parlerons vous parlerez elles parleront 5 8 Second go to fut word make pronouns je tu il nous vous elles make endings lai as a ons ez ont make i 0 repeat 6 make i i 1 pr se item i pronouns word word item end fut parler je parlerai tu parleras il parlera nous parlerons vous parlerez elles parleront 5 9 Or even A little recursion to fu verb make pronouns je tu il nous vous elles make endings ai as a ons ez ont conjugate verb pronouns endings end 47 i endings to conjugate verb pronouns endings if empty pronouns stop pr se first pronouns word verb first endings conjugate verb bf pronouns bf endings end fu parler je parlerai tu parleras il parlera nous parlerons vous parlerez elles parleront 5 10 All about colours 5 11 Introduction Fist a few explanations you will note that the command setpc can take either a list or a number as a parameter Here we are interested in coding RGB values Every colour in XLOGO is coded using three values red green and blue whence the name RGB encoding The three numbers in the list parameter to the primitive setpc therefore represent respec tively the red blue and green components of a colour This encoding is not really intuitive and you can get an idea of the colour which will be given by the encodin
7. and increase its size again e To use the JRE 1 4 1_07 proposed on the website With JRE gt 1 5 it seems better 7 5 How to type quickly a control used previously e First method with the mouse click on the line in the historic area it will reappear immediately on the control line 53 7 6 Second method with the keyboard the UP and Down arrows allow to navigate through the list of the last controls that have been typed very practical How can you be helped By reporting any observed bug If you are able to reproduce systematically an observed problem it is even better Any suggestion to improve the program is welcome By helping to translate in English especially A little moral support is always welcome 54 Index absolute abs 17 additem 19 and 18 animation 13 appendlineflow 26 arc 12 arccosine acos 17 arcsine asin 17 arctangent atan 17 back bk 12 before 21 black 11 blue 11 brown 11 butfirst bf 19 butlast bl 19 changedirectory cd 25 character char 20 chattcp 41 circle 12 clearscreen cs 13 cleartext ct 16 close 14 closeflow 26 colortext ctext 16 cosine cos 17 count 20 countdown 39 cyan 11 darkblue 11 darkgreen 11 darkred 11 date 39 define def 24 deletesequence delseq 31 difference 17 directory dir 25 distance 14 div divise 17 dot 13 empty 21 end 22 endcountdown 39 endflow 26 equal 21 erall
8. second tab you can choose your preferred turtle On the third tab many options On You can choose the maximal pen width allowed If you don t want to use this option put 1 You can choose the shape of the pen round or square You can choose the maximal number of turtle in mode multiturtle You can choose if you want to clear screen when you leave the editor You can choose a personal size for the drawing zone Otherwise XLogo opens in 1000 on 1000 pixels zone Be careful when you increase the size of the image you might have to increase the memory size of XLogo An error message will pop up Consequently you can also change the corresponding memory space allocated to XLogo Otherwise it will be a 64 Mo size You might have to increase it if you want to work on a bigger drawing zone When you modify this parameter you must restart XLogo so that the change takes place Be careful do not over increase this parameter since it could considerably slow your system down Finally you can choose the accuracy of the drawing line In high quality definition you will especially not have the square effect Yet do not forget that by increasing the quality you will lose some execution speed the fourth tab you can choose an instrument for your MIDI interface Some prob lem of detection can appear sorry This function could be accessed with the primitive setinstrument On the fifth tab You
9. showturtle st none Makes the turtle invisible on the screen hideturtle ht clearscreen cs SE none Erases the drawing area but leaves the turtle in the same place gereit p The turtle will draw a line when it moves The turtle will not draw a line when it moves none The turtle will rub out any marks that it meets penerase pe none Lower the pen and put the turtle in inverted mode er er none Lower the pen and put the turtle in classic drawing penp PP node true or false animation e if the argument is true you go into animation mode The turtle does not draw on the screen anymore but follows the stored line To up date the drawing on the screen use the primitive update It is very useful to create an animation or to draw a line faster If the argument is false you switch back to classical mode You can see the turtle s moves on screen 13 GEES none In animation mode updates the screen the image on repaint f the drawing area is updated a whole num Sets the pen color See p 11 t 1 is i setpencolor Setpc ber or list r 8 a whole num Sets the screen color See p 11 setscreencolor b list SE er or list r g Gives the current position of the turtle Eg pos re turns 10 100 Gives the bearing or heading of the turtle cf setheading The list must contain two numbers representing co ordinates Gives the heading which the turtle must fol low to go towards the point de
10. usage of these two primitives in the examples at the end of this manual 4 11 Multiturtle Mode It s possible to have several active turtles on the screen By default on Xlogo startup only one turtle is available Its number is the 0 If you want to create a new turtle you can use the primitive setturtle followed by the number of the turtle To prevent from obstruction the turtle is created on the origin and is invisible you must use showturtle to show it Then the new turtle is the active turtle it obeys to all classic primitives while you don t change active turtle with setturtle The maximum number of available turtle can be set in menu Options Preferences Tab options Here are the primitives for the multiturtle mode 30 Argumentss Utilisation a number The turtle numero a is now the active turtle By de fault on Xlogo startup the active turtle is the numero 0 none Returns the numero of the active turtle turtle none Returns a list which contains all the numero af the turtles turtles actually on the screen a number Kill the turtle number a killturtle 4 12 Play music a list Put in memory the sequence in the list Read after Pedy POQUe es this table to learn how to write a sequence none Play the sequence in memory play none Returns the number that corresponds to the selected instr instrument instrument a number The selected instrument is now the instrument number sinstr a You can see the list of
11. 0 repeat 2 fd 50 rt 90 fd 100 rt 90 rt 45 pu fd 10 pd setpc 255 153 153 fill bk 10 1t 45 pd setpc 0 end to lance cs button pu setpos 150 0 pd button pu setpos 30 20 pd label Square pu setpos 180 20 pd label Circle pu setpos 0 100 pd mouse end to mouse we put the value of readmouse in the variable ev make ev readmouse we put the first coordinate of the mouse in variable x make x item 1 posmouse we put the second coordinate of the mouse in variable y make y item 2 posmouse When we click on the left button if ev 1 amp x gt 0 x lt 100 amp y gt 0 y lt 50 square When we click on the right button if x gt 150 x lt 250 amp y gt 0 y lt 50 if ev 1 circle if ev 3 stop mouse end to circle repeat 90 fd 1 1t 4 1t 90 pu fd 40 rt 90 pd end to square repeat 4 fd 40 rt 90 rt 90 fd 40 1t 90 end 38 4 15 Time and date XLogo has several primitives for date time or generating countdown f n whole num Halts the program and therefore the turtle for 7 wait ber seconds n integer Starts a countdown of n seconds We know chrono A i A D if this countdown has finished with the primitive chronometre endcountdown none Returns true if there s no active countdown Returns endcountdown e false if the countdown is active none Returns a list wich contains three integers represent date P ae ing the date The first integer indicates the da
12. 00 rt 90 or executetcp turtle repeat 4 fd 100 rt 90 e chattcp Allows chat between two computers on a network On each computer it displays a chat window Syntax chattcp word list gt The word is the called IP address or computer name the list contains the sentence to display Example hare wants to talk with turtle First turtle executes listentcp so it is waiting for instructions from network computers Then hare writes chattcp 192 168 1 2 hello turtle Chat windows will open on both computers allowing them to talk with each other e sendtcp Send data towards a computer on the network and return his answer Syntax sendtcp word list gt The word is the called IP address or computer name the list contains the data to send When Xlogo is launched on the other computer il will answer OK It is possible with this primitive to communicate with a robot through its network interface Then the answer of the robot could be different Example turtle wants to send to hare the sentence 3 14159 is quite pi First hare executes listentcp so it is waiting for the other computer to communicate Then turtle writes print sendtcp hare 3 14159 is quite pi A little hint Launch two instances of XLogo on the same computer In the first window execute listentcp In the second one write executetcp 127 0 0 1 fd 100 rt 90 You can move the turtle in the other window heh heh it s possible because 127 0 0 1 design
13. IP address of the first computer in the illustration is 192 168 1 1 Because it s not easy to remember these numbers it s also possible to identify each computer by a more usual name As can be seen in the illustration we can communicate to the right computer with its IP address 192 168 1 2 or with its name turtle For the moment Pll add just one more thing The local computer on which you are working is located by the address 127 0 0 1 Its general name is localhost We will see this later in practice 4 16 2 Primitives for networking XLogo has 4 primitives that allow it to communicate over a network listentcp executetcp chattcp and send In all future examples we will take the case of the two computers in the previous figure e listentcp this primitive listentcp is the basis for all network communication It doesn t need an argument When you execute this primitive on a computer the computer will listen for instructions sent from other computers on the network e executetcp this primitive allows execution of instructions by a computer on the network Syntax executetcp word list gt The word is the called IP address or computer name the list contains instructions to execute Example I m on computer hare I want to draw a square with a side of 100 on the other 40 computer Thus on the computer turtle I have to launch the command listentcp Then on the computer hare I write executetcp 192 168 1 2 repeat 4 fd 1
14. O fait de la retouche d images make g first list make list bf list make b first list make b round r g b 3 output se list b b b end to greyscale c if y 100 stop if c 100 make c O make y y 1 We assign the average colour of the following pixel to the pen setpc pixel fc liste c y We turn the dot to greyscale dot list c y greyscale c 1 end to transform You must change the path to the image transfo png Eg setdir c my_images loadimage transfo png cs ht setdir home loic loadimage transfo png make y O greyscale 0 end 5 13 And if you want a negative To change an image to a negative you can use the same process except that instead of averaging the numbers r g b you replace them by the number you get when you subtract them from 255 Eg If a pixel has the colour 2 100 200 you replace it with the colour 253 155 55 Only the pixel procedure needs to be changed in the following program to greyscale c if y 100 stop if c 100 make c 0 make y y 1 setpc pixel fc list c y 49 AV ANT APRES Figure 5 6 XLOGO pretending to be the GIMP pretentious dot list c y greyscale c 1 end to transform You must change the path to the image transfo png Eg setdir c my_images loadimage transfo png ht cs setdir home loic loadimage transfo png make y 0 greyscale 0 end to pixel list make r first list make list bf list ma
15. XLOGO User Manual Author Le Coq Loic Translated by Walker Guy Donnelly Kevin Roch Etienne April 19 2007 Contents Interface features Li The main WindOW e eae pedea oe ae A e A ce Ae a een da 1 2 The procedure editor se saie ask ee Menu options ST File Men iros ces eo ae ee ee ee eR a A ST Edit Mens s 2 cier koa ea aaa ee Ee ee ee 2 3 Options Meng sast em 3000584080005 Bab ee Pea bee ee ee g 2A Help Menu ss ea 34 re 204 cob me Ga ae eee eR aw ae ae ed A Conventions adopted by XLOGO 3 1 Commands and their interpretation 2 ee 3 2 Procedures canssa es e eee Re ES Ee ee ee ee eS 3 3 Specific character Y ops esa kon ee bee ooo EDR o a a A 3A Cas Sensitivity isa aa aA ee a eee ee ew a ee 3 5 Operators and syntax e sas eog ee 3 6 A word on colors 2 44 5 6 h4 2 eo eee pe eG hg ee hee oe RE SRS Ea EAs List of primitives 4 1 Movement of the turtle pen and colour settings 0 e e 4 2 Writing in the text area with the primitive print or write 4 3 Arithmetical and logical operations 2 2 a AA Operations on lists e e e sa meag bie me de ee eee eae eh a 45 Booleans 5540254425 4 AS HAM ER EER eee he Re da 4 6 Testing an expression with the primitive if 200 4 7 Dealing with procedures and variables e Ad Procedures s y a 452 064 e ee eee er e ae we aoe Be ele whe e 41 2 Concept ot variables ui ia wae Be e oe
16. all available instruments in BERENS menu Options Preferences Tab Sound sturtle setturtle none Returns where the cursor is located in the current se indseq quence indexsequence a number Put the cursor to index a in the current sequence in memory sindseq setindexsequence none Delete the current sequence in memory delseq deletesequence If you want to play music you must put the notes in memory in a list called sequence To cre ate the sequence you can use the primitive seq or sequence These are rules to follow to create a valid sequence do re mi fa sol la si the usual notes of the first octave To make a sharp re we note re To make a flat re we note re If you want to go up or down and octave we use symbol followed by or E g After in the sequence all the notes will be played two octaves up two By default notes are played for a duration of one If you want to increase or decrease you write the number that corresponds to the duration of notes E g seq sol 0 5 la si will play sol with a duration 1 and la si with a duration 0 5 twice faster If you want to play this example 31 to tabac create the sequence of notes seq 0 5 sol la si sol 1 la 0 5 la si 1 do do si si 0 5 sol la si sol 1 la 0 5 la si 1 do re 2 sol seq 1 re 0 5 re do 1 si 0 5 la si 1 do re 2 la seq 1 re 0 5 re do 1 si 0 5 la si 1 do re 2 la seq 0 5 sol
17. alse a boolean Returns the negation of a If a is true returns false not If a is false returns true 18 4 4 Operations on lists Primitives Parameters Usage ae 222 Concatenates the two words a and b Eg pr word a 1 returns al Returns a list composed of a and b For example list 3 6 returns 3 6 list a list returns a list Returns a list composed of a and b If a or b is a list sentence Sg then each element of a and b will become an element of the resulting list square brackets are deleted Eg se 4 3 hello returns 4 3 hello se how are things returns how are things Insert a in the first slot in list b fput thing b list Eg fput cocoa 2 returns cocoa 2 a b a any Insert a in the last slot of list b CES thing b list Eg lput 5 7 9 5 returns 7 9 5 5 a list Reverse the order of elements in list a reverse o TT reverse 1 2 3 returns 3 2 1 a a word or Ifa is a word returns one of the letters of a at random a b a any Remove element a from list b if it occurs there remove thing b list Eg remove 2 1 23426 returns 1 3 4 6 a b a whole If b is a word returns the letter numbered a from the item number b list word 1 represents the first letter If b is a list returns or word the element numbered a from the list a list or word If a is a list returns the whole list except for its last butlast bl element Ifa is a word returns the word minus its last lette
18. are two kinds of variables e Global variables these are always accessible from any location in the program e Local variables these are only accessible in the procedure where they are defined In this version of LOGO local variables are not accessible in sub procedures At the end of the pro cedure the local variables are deleted 4 7 3 Primitive trace It is possible so as to follow the working of a program to have it show the procedures which are working This mode equally allows to show if the procedures provide arguments thanks to the primitive output To operate this mode you type trace true Of course trace false will disactivate the trace mode A small example with the factorial see page 44 trace vrai pr fac 4 fac 4 fac 3 fac 2 fac 1 fac returns 1 fac returns 2 fac returns 6 fac returns 24 24 23 4 7 4 Other primitives ms a b a word b If the local variable a exists assigns it the value b If anything not creates a global variable a and assigns it the value b Eg make a 100 assigns the value 100 to the variable a Creates a variable called a Note this is not initialised To assign it a value see make E Fe Pl localmake anything b Define a new procedure called wordl whic requires the variables in list2 The procedure s instructions are contained in list3 def polygon nb length def define SEN list2 repeat nb fd length rt 360 nb gt this command defines a procedu
19. ates your local address so it s your own computer 41 Chapter 5 Program examples 5 1 Draw houses fh Figure 5 1 Houses to house c repeat 4 fd 20 c rt 90 fd 20 c rt 30 repeat 3 fd 20 c rt 120 end to place c pu lt 30 bk c 20 rt 90 fd c 22 lt 90 pd 42 end to hut cs pu lt 90 fd 200 rt 90 pd ht house 3 place 3 house 5 place 5 house 7 place 7 house 10 end 43 Figure 5 2 Rectangle 5 2 Draw a whole rectangle to rect lo la if lo 0 la 0 stop repeat 2 fd lo rt 90 fd la rt 90 rect lo 1 la 1 end 5 3 Factorial Reminder 51 5x4x3x2x1 120 to fac n if n 1 output 1 output n fac n 1 end por fac 5 120 0 pr fac 6 720 0 5 4 The snowflake with thanks to Georges No l to koch order len if order lt 1 len lt 1 forward len stop koch order 1 len 3 lt 60 koch order 1 len 3 rt 120 koch order 1 len 3 lt 60 koch order 1 len 3 end 44 Figure 5 3 The snowflake to kochflake order len repeat 3 rt 120 koch order len end kochflake 5 450 45 o a a TL mp Lo Si 3 CH pr Figure 5 4 Xlogo c est sympa 5 5 A little bit of writing to write ht repeat 40 fd 30 rt 9 setpc random 7 label xlogo is cool end 46 5 6 And conjugation 5 7 First version to Fr_future word pr se je word word ai pr se tu word word as pr se il word word a pr se nous word word ons pr se vous word
20. b power n number returns the square root sqrt sqrt n number Returns the decimal logarithm of n log10 a number Returns the sine of a a is expressed in degrees sin sine a number Returns the cosine of a a is expressed in degrees cos cosine a number Returns the tangent of a a is expressed in degrees tan tangent a number Returns the angle in range 0 180 which cosine is a acos arccosine a number Returns the angle which sine is a asin arcsine a number Returns the angle which tangent is a atan arctangent Returns the number 7 3 141592653589793 pi n whole num Returns a random number between 0 and n 1 random ran ber n nombre Returns the absolute value its numerical value with absolute abs out regard to its sign of a number Important Be careful with those primitives which require two parameters Eg setxy ab _ If b is negative For example setxy 200 10 The logo interpreter will carry out the operation 200 10 ie it will subtract 10 from 200 It will therefore conclude that there is only one parameter 190 when it requires two and will generate an error message To avoid this type of problem use the primitive minus to specify the negative number setxy 200 minus 10 This is a list of logical operators Primitives Parameters Usage b booleans Returns true if a or b is true otherwise returns false or PP ae Returns true if a and b is true otherwise returns f
21. can choose the font for the interface Help Menu e Menu gt Licence shows the GPL license under which this software is distributed e Menu gt Translation shows a translation of the above license This translation has no official standing this belongs only to the English version and the translation is provided here only as an aid to understanding e Menu gt About The standard thing and xlogo tuxfamily org for your bookmarks oi Chapter 3 Conventions adopted by XLOGO This section sets out some key points about the LOGO language itself and about XLOGO specifically 3 1 Commands and their interpretation The LOGO language allows certain events to be triggered by internal commands these commands are called primitives Each primitive may have a certain number of parameters which are called arguments For example the primitive cs which clears the screen takes no arguments while the primitive sum takes two arguments print sum 2 3 will return 5 LOGO arguments are of three kinds e Numbers some primitives expect numbers as an argument fd 100 is an example e Words Words are marked by an initial An example of a primitive which can take a word argument is print print hello returns hello Note that if you forget the the interpreter will return an error message In effect print expects the argument or for the interpreter hello does not represent anything since it is not a number a
22. e name of the font list or word Set the format of the police in the text area You can choose between seven styles none bold italic strike underline superscript subscript If you want several styles together write them in a list Look at examples after this table none Returns a list which contains the differents styles used style sty for the primitive print A few examples for formatting text setstyle ssty setstyle bold underline print hello hello ssty strike write strike ssty italic write x ssty superscript print 2 strike x 16 4 3 Arithmetical and logical operations Primitives Parameters a b numbers Adds the two numbers a and b and returns the result to add Eg sum 40 60 returns 100 a b numbers Returns a b difference Eg difference 100 20 returns 80 a number Returns the negative of a minus Eg minus 5 returns A See the note at the end of this table ab numbers Returns the result of multiplying a by b product a b numbers Returns the result of dividing a by b div divise div 36 returns 0 5 a b numbers Returns quotient a by b quotient quotient 15 6 returns 2 a b whole Returns the remainder after dividing a by b remainder numbers a number Returns the nearest whole number to the number a round rnd round 6 4 returns 6 a number returns the integer part of the number integer 8 9 integer returns 8 integer 6 8 returns 6 a b numbers Returns a raised to the power of
23. e successive values in a fixed range with a choosen increment here is the syntax for Uert list2 List1 contains three arguments the variable name the start value the end value A fourth argument is optionnal representing the increment the step between two successive values Default value is 1 Here are a few examples for i 1 4 pr i 2 2 4 6 8 Now i is going from 7 to 2 falling down of 1 5 each times Look at the negative increment Then Displays its square for i 7 2 1 5 pr list i power i 2 7 49 5 5 30 25 4 16 2 5 6 25 33 4 13 3 A loop with while This is the syntax for while while list_to_evaluate list_of_commands list_to_evaluate is a list containing an instruction set which can be evaluated as a boolean list_of_commands is a list containing the commands to execute The LOGO interpreter will continue implementing the list_of_commands so long as the list_to_evaluate is returned as true Eg while true rt 1 The turtle will turn around An example which allows us to spell the alphabet in reverse make list abcdefghijklmnopqrstuvwxyz while not empty list pr last list make list butlast list 34 4 14 Receiving input from the user 4 14 1 Interact with the keyboard Currently text can be accepted from the user during program execution mainly via 3 primitives key readchar and read key is read as true or false according to whether a key has been pressed or not
24. eadlineflow i number used as argument and then reads a line in this file id Opens the flux which identifier corresponds to the readcharflow number used as argument and then reads a charac ter in this file This primitive sends back a num ber representing the value of the character similar to readchar id list Writes the text line included in the list at the begin itelinefl Kee ning of the file identified thanks to the identifier id Be careful the writing is effective only after the flow has been closed by the primitive closeflow id list Writes the text line included in the list at the end of the file identified thanks to the identifier id Be careful the writing is effective only after the flux has been closed by the primitive closef low id Closes the flux when its identifier number is written closeflow as argument id Sends back true if it is the end of the file Otherwise endflow sends back false Here is an example of the use of primitives allowing to read and write in a file I will give this example in a Windows type framework Other users should be able to adapt the following example appendlineflow The aim of this file is to create the file c example containing the following three lines ABCDEFGHIJKLMNOPQRSTUVWXYZ Abcdefghijklmnopqrstuvwxyz 0123456789 You open a flow towards the desired file This flow is given the number 2 setdirectory c openflow 2 example You type the desired lines
25. ered and the associated response To quickly recall a command which has already been entered there are two options you can either click on the old command in the history or you can click several times on the upper scroll arrow until the desired command appears The upper and lower scroll arrows in fact allow you to navigate through all the commands that you have already entered very practical e To the right of the history are two buttons STOP and EDITOR STOP interrupts the execution of the program and EDITOR allows the procedure editor to be opened 1 2 The procedure editor There are three ways to open the editor e Enter ed on the command line at the top of the screen The editor will then open to show all the procedures already defined If you only want to edit specific procedures enter ed procedure_1 procedure_2 e Press the Editor button on the main screen e Use the keyboard shortcut Alt E These are the different buttons that you will find in the editor Save the changes made in the editor and then close it It is this button that you have to press each time you want to apply newly entered operations If you prefer you can use the keyboard shortcut ALT Q Quit the editor without saving any of the changes made there You can also use the shortcut ALT C Print the contents of the editor Copy the selected text to the clipboard SEI oO E Cut the selected text to the clipboard TR d Paste the selected te
26. ession_test listi list2 if expression_test is true the instructions included in list1 are executed Else if expression_test is false the instructions in list2 are executed This second list is optional Examples e if 1 2 3 print true print false e if first XLOGO Y fd 100 rt 90 pr XLOGO starts with a X e if 3 4 6 6 pr 12 4 7 Dealing with procedures and variables 4 7 1 Procedures Procedures are a kind of program When a procedure is called the instructions in the body of the procedure are executed A procedure is defined with the keyword to to name_of_procedure vil wi v3 Body of the procedure end name_of_procedure is the name given to the procedure v1 v2 v3 stand for the variables used internally in this procedure local variables Body of the procedure represents the commands to be executed when this procedure is called Eg to square s repeat 4 fd s rt 90 end The procedure is called square and takes a parameter called s square 100 will therefore produce a square the length of whose sides is 100 See the examples of procedures at the end of this manual Since version 0 7c it is possible to insert comments in the code preceded by to square s this procedure allows a square to be drawn whose side equals s repeat 4 fd s rt 90 handy isn t it end IMPORTANT There must be no comments on the to or end lines 22 4 7 2 Concept of variables There
27. fined by the co ordinates in the list The list must contain two numbers representing co ordinates Gives the number of steps between the cur rent position and the point defined by the co ordinates in the list Gives the current colour of the pen This colour is specified by a list r g b where r is the red component b the blue and g the green Gives the current colour of the screen background This colour is specified by a list r g b where r is the red component b the blue and g the green The turtle can travel outside the drawing area but of course it cannot draw there If the turtle leaves the drawing area it will reappear on the opposite side The turtle is confined to the drawing area If it is about to go outside an error message will let you know and give you the maximum number of steps the turtle can move before the exit point is reached to within 1 or 2 steps Returns to the colour of the a coordinates pixel This color is determined thanks to a r g b list where r is red g is green and b is blue Defines the thickness of the pen nib in pixels The default is 1 The pen has a square nib Other shapes will be provided in future versions You can choose your preferred turtle with the sec ond tab of menu Options Preferences But you can choose your favourite turtle with setshape The num ber n goes from 0 to 6 0 is the triangular shape setshape 14 GEES none Returns the number that
28. g by using the dialogue box Options gt Choose the pen colour Using this encoding it is very easy to transform an image For example if you want to turn a colour photo into a greyscale image you can change the colour of each pixel of the image to the average value of the three components r g b Imagine that the colour of one dot of the image is given by the encoding 0 100 80 You calculate the average of these three numbers i 60 and then assign the colour 60 60 60 to this pixel This operation has to be carried out on each pixel of the image 5 12 Let s get practical We are going to transform a 100 x 100 pixel image to a greyscale This means that there are thereforel00 x 100 10000 pixels to modify You can access the image used in this example at the following address http xlogo tuxfamily org images transfo png This is how we are going to proceed first we will refer to the top left corner of the image as 0 0 Then the turtle will examine the first 100 pixels of the first line followed by the first 100 of the second line and so on Each time the colour of the pixel will be retrieved with findcolor and the colour will then be changed to the average of the three r g b values Here is the relevant code Don t forget to change the filepath in the transform procedure to pixel list return the average of three numbers r g b make r first list make list bf list 48 AY ANT APRES Figure 5 5 XLOG
29. have a problem with installation or use All suggestions are welcome 52 Chapter 7 FAQ Tricks Things to know 7 1 Though I erase a procedure from the editor it keeps on popping back When you go out of the editor it just saves or updates whet the editor contains The only way to erase a procedure in XLogo is to use the primitive erase or er Exemple erase toto gt erase the procedure toto 7 2 Pm using the version in Esperanto but I can t write with the special characters When you type in the command line or the editor if you click with the right button a rolling screen appears In this menu you can find the traditional editing functions cut copy paste and the esperanto special characters when this language is selected 7 3 In the Sound tab from the Preferences dialogue box no instru ment can be found Sorry this problem has already been spotted It is because of the java virtual machine This problem is totally random For example in my case I have a computer which works with Linux and Win 98 With Win 98 the list doesn t appear and with Linux it does And I m using the same JRE and have no material problem This may change from a JRE version to another 7 4 I have screen updating problems when the turtle is drawing This is also a known problem of the JRE I will try to deal with it in the future I might be able to do something about it For now there are two solutions e to minimize the window
30. initial position that is the co ordinates 0 0 with a heading of 0 degrees x y list of Moves the turtle to the co ordinates specified by the setpos two nunbers two numbers in the list x specifies the x axis and y the y axis ae X X axis Moves the turtle horizontally to the point x on the X axis Moves the turtle vertically to the point y on the y axis x y Satay X y x co Identical to setpos x y ordinate followed by y co ordinate 12 n heading or Orients the turtle in the specified direction 0 corre bearing sponds to a position facing vertically upwards The heading when the turtle is rotated is then based on compass bearings Tabel a word or list Draw the specified word or list at the turtle s location and following the direction it is facing Eg label Hello there will write the sentence Hello there wherever the turtle is and corresponding to its bearing or heading setheading a word or list Returns the length that needs the word or the list to labellength re be displayed on the screen with the primitive label using the current font Jot a list The point defined by the co ordinates in the list will be highlighted in the pen colour This second table sets out the primitives which allow the properties of the turtle to be adjusted For example should the turtle be visible on screen What colour should it draw when it moves CO none Makes the turtle visible on the screen
31. ke g first list make liste bf list make b first list output se list 255 r 255 g 255 b end 5 14 A good example of using lists with thanks to Olivier SC I hope you will appreciate this wonderful program to reversew w if empty w output output word last w reversew bl w end to palindrome w if equal w reversew w output true output false end 50 Figure 5 7 Better than using a compass to palin n if palindrome n print n stop print se se se se n more reversew n equal sum n reversew n palin n reversew n end palin 78 78 more 87 equal 165 165 more 561 equal 726 726 more 627 equal 1353 1353 more 3531 equal 4884 4884 5 15 A pretty rosette to rosette repeat 6 repeat 60 fd 2 rt 1 rt 60 repeat 120 fd 2 rt 1 rt 60 end to pretty_rosette rosette repeat 30 fd 2 rt 1 rosette repeat 15 fd 2 rt 1 rosette repeat 30 fd 2 rt 1 rosette end setsc 0 cs setpc 5 ht rosette pu setpos 300 0 pd setheading 0 pretty_rosette ol Chapter 6 Uninstall and bookmark 6 1 Uninstall To uninstall XLogo all that needs to be done is to delete the file XLogo jar and the configuration file xl ogo which is located in your home directory home your_login for Linux users or c windows xlogo for Windows users 6 2 Bookmark For the latest version and bug fixes visit the XLogo site now and again http xlogo tuxfamily org Feel free to contact the author is you
32. la si sol 1 la 0 5 la si 1 do do si si 0 5 sol la si sol 1 la 0 5 la si 1 do re 2 sol end To hear music launch the command tabac play Now we can see an interesting application of the primitive sindseq Write those commands delseq Delete the sequence in memory tabac Put in memory the notes sindseq 2 Put the cursor on the second la tabac Put in memory the same sequence but translated of 2 play Great You can choose you instrument with the primitive sinstr or with the menu Options Preferences Tab sound You will find the list of all available instruments with their associated number 32 4 13 Loops XLOGO has three primitives which allow the construction of loops repeat for and while 4 13 1 A loop with repeat This is the syntax for repeat repeat n list_of_commands n is a whole number and list_of_commands is a list containing the commands to execute The LOGO interpreter will implement the commands in the list n times that avoids the need to copy the same command n times Eg repeat 4 forward 100 left 90 A square of side 100 repeat 6 forward 100 left 60 A hexagon of side 100 repeat 360 forward 2 left 1 A uh 360 gon of side 2 In short almost a circle Included in a repeat loop Its an internal variable Returns the number of the running iteration The first iteration is number 1 repeat 3 pr repcount 1 2 3 4 13 2 A loop with for for assign to a variable som
33. nt b the blue and g the green Xlogo has 16 predefined colours you can access with their rgb list with a number or with a primitive look at this table RGB OA red 255 0 0 0 255 0 255 255 0 0 0 255 255 0 255 0 255 255 255 255 255 128 128 128 192 192 192 128 0 0 0 128 0 0 0 128 255 200 0 255 175 175 128 0 255 153 102 0 These three instructions are the same setsc orange setsc 13 setsc 255 200 0 11 Chapter 4 List of primitives As noted above the turtle is controlled by means of internal commands called primitives The following sections set out these primitives 4 1 Movement of the turtle pen and colour settings This first table sets out the primitives which govern the movement of the turtle ization n number of Moves the turtle forward n steps in the direction it is forward fd steps currently facing back BE n number of Moves the turtle backwards n steps in the direction it steps is currently facing n angle Turns the turtle n degrees towards the right in relation right rt i SE to the direction it is currently facing left 1t n angle Turns the turtle n degrees towards the right in relation to the direction it is currently facing Draws a circle of R radius around the turtle circle BE R capl cap2 Draws an arc of R radius around the turtle This arc numbers is inscribed between the caps cap and cap2 home any Returns the turtle to its
34. pixels with the current pen colour If for example you type setpc 1 fill Let s now go back Figure 4 2 With the primitive fill to the first case if the pen colour of the turtle is black the primitive fillzone colours all pixels until it encounters the current colour here black This is a good example of the use of this primitive to halfcirc c draw a half circle of diameter c repeat 180 fd c tan 0 5 rt 1 fd c tan 0 5 rt 90 fd c end 28 Figure 4 3 With the primitive fillzone if you type setpc 0 fillzone to tan angle renders the tangent of the angle output sin angle cos angle end to rainbow c if c lt 100 stop halfcirc c rt 180 fd 20 1t 90 rainbow c 40 end to dep pu rt 90 fd 20 1t 90 pd end to arc ht rainbow 400 pe 1t 90 fd 20 bk 120 ppt pu rt 90 fd 20 pd setpc O fill dep setpc 1 fill dep setpc 2 fill dep setpc 3 fill dep setpc 4 fill dep setpc 5 fill dep setpc 6 fill dep end 29 Figure 4 4 Arc in LOGO 4 10 Break commands LOGO has three break commands stop stopall and output e stop can have two results If it is included in a repeat or while loop the program jumps out of the loop then and there If it occurs in a procedure the program breaks out of the procedure immediately e stopall the program breaks out of all the procedure immediately and stops e output allows breaking out of a procedure with a value to be returned See the numerous instances of
35. r a list or word If a is a list returns the whole list except for its first butfirst bf element If a is a word returns the word minus its first letter a list or word If a is a list returns the last element of the list If a prose edad PRA e a list or word If a is a list returns the first element of the list If a CO i a word nro the Aest rf the morde o lil n li2 lil Replace the element number n in the list li by the list n integer word or the list 112 li2 word or list setitem replace replace a b c 2 8 gt a 8 c lil n l2 lil Adds at the position n in the list 1i the word or the list n integer list 1i2 li2 word or list additem additem a b c 2 8 gt a 8 b c 19 a list or word If a is a word returns the number of letters in a If a count is a list returns the number of elements in a a word returns the Unicode value of the character a unicode pr unicode A returns 65 a number returns the character which Unicode value is a character char pr character 65 returns A 20 4 5 Booleans A boolean is a primitive which returns the word true or the word false These primitives terminate in a question mark Primitives Parameters Usage none Returns true true none Returns false false Returns true if a is a word false otherwise word Returns true if a is a number false otherwise number returns true if a is a whole number false otherwise
36. rd and stop with Esc 4 14 3 Interact with the mouse Currently mouse events can be accepted from the user during program execution via three primitives readmouse posmouse and mouse readmouse the program is paused until the user presses the mouse Then it returns a number that represents the event These are the differents values 0 gt The mouse has moved 1 gt The button 1 has been pressed 2 gt The button 2 has been pressed The button 1 is the left button the button 2 is the next on the right posmouse Returns a list that contains the position of the mouse mouse Returns true if we touch the mouse since the program begins Returns false otherwise 4 14 4 Some examples of usage In this first procedure the turtle follows the mouse when it moves on the screen to example when the mouse moves go to the next position if readmouse 0 setpos posmouse example end In this second procedure it s the same but you must click with the left button of the mouse if you want the turtle to move to example2 if readmouse 1 setpos posmouse example2 end In this third example we create two pink buttons If we left click on the left button we draw a square with a side of 40 if we left click on the right button we draw a little circle Last if we right click on the right button it stops the program 36 Yooodedded to button create a pink rectangular button height 50 width 10
37. re called polygon with two variables nb and length This procedure draws a regular polygon we can choose the number of sides and their length f a word returns the value of the variable a thing a is simi thing lar to a Deletes all the variables and procedures currently run ning Enumerates all the procedures currently defined a list Executes the list of instructions contained in list a i none Returns a list which contains all the defined variables listvariables lvars 24 4 8 File handling i none By default lists the contents of the directory Equiv ls listfiles e alent to the ls command for Linux users and the dir command for DOS users a list Load the image file contained in the list Its upper left loadimage li A corner will be placed at the turtle s location The only supported formats are png and jpg The path speci fied must be relative to the current folder Eg setdir C my_images_dir loadimage turtle jpg l list Specifies the current directory The path must be ab setdir z f solute The directory must be specified with a word setdirectory m word Allows to choose the current directory The path is related to the current directory You can use the notation to refer to the parent directory d r director aucun Gives the current directory The default is the user s y home directory ie home your_login for Linux users C WINDOWS for Windows users
38. represents the shape of the enaps turtle n number When you write on the screen with the primitive label it s possible to modify the size of the font with setfontsize The size of the font is 12 by default none Returns the size of the font when you write on the fontsize A Battie screen with the primitive label n number Select the font number n when you write on the screen with the primitive label You can find the link be tween number and font in Menu gt Options gt Pref erences gt Tab Font setfontsize setfs setfn setfontname Returns a list with two elements The first is the num ber corresponding to the font used when you write on the screen with the primitive label The last element is a list which contains the name of the font a number Determines the ratio between the graphic screen and the history zone The number a must be included between 0 and 1 When a equals 1 the drawing zone uses all the space when a equals 0 the history zone uses all the window aia Ss none Provides the current ratio between the drawing zone P SES and the history zone none Returns a list which contains four numbers These zonesize f integers are the coordinates of the left upper corner of the drawing zone and the coordinates for the right bottom corner message msg a list Shows the message in list in a dialog box the program stops until the user has clicked the button OK 4 2 Writing in the text area
39. rsion ee 5 10 AN about colours 2 2 42 64 aa bee Ga ee eee be A ee ee A a a Bld Introduction 4 6 28 Sy wih ea a Ae RS wth e 5 12 Let s get practical 2 2 5 ai a ara doe Boies eee a E RD aoe he a ee ee ed 5 13 And if you want a negative 2 2 ee 5 14 A good example of using lists with thanks to Olivier SC 5 15 A pretty Tosette c eme ma ee we ee aR a ee A a et Uninstall and bookmark GH Uninstall gsc ler gie Genie wage e ek a Ge We rd el ee dae 6 2 Bookmark s do sarao A ee ee Ee bee ee ee ke A e FAQ Tricks Things to know 7 1 Though I erase a procedure from the editor it keeps on popping back 7 2 I m using the version in Esperanto but I can t write with the special characters 7 3 In the Sound tab from the Preferences dialogue box no instrument can be found 7 4 I have screen updating problems when the turtle is drawing 7 5 How to type quickly a control used previously ooo 7 6 How can you be helped e 42 42 44 44 44 46 AT AT AT 47 48 48 48 49 50 ol 52 52 52 Chapter 1 Interface features 1 1 The main window e Along the top there are the usual menus File Edit Options and Help e Just below this is the command line which allows the logo instructions to be applied e In the middle of the screen is the drawing area e At the bottom is the command history which shows every command ent
40. s Se doce e ver dea Primitive trace exentas edi ENEE e a ee dor Other primitives dis e da ld ee A we Oe A 4 8 Paie handling 0 000 a a ca de AO a eee Oe DE Re eee eo 4 9 Advanced fill function 2 u mee 24 ee wa ee a Re ee ee 4 10 Break commands 4 4 sred goa eRe ae E e eee EE Se es 4 11 Multiturtle Mode 412 Play Musics NA AUS LOOPS isa bf ha he he cs PR Be Be ee EY abe Ooh ee Bed Se ag ed 4 13 1 A loop with 6peat ss yay ee beh he de Eh ee D GOS 4 13 2 A loop with for lt s sss bo eee biena ew EG wa ee ke ore 4 13 3 A loop With while e a w Co ov or or CO O CO CO 9 4 14 Receiving input from the user ee 4 14 1 Interact with the keyboard 0 02 2000 0 ee eee 415 Time and date cos a sb da A ceeded NR ana e RS ge diia 4 16 Using a network with Silo 4 16 1 The network Howto ee ee 4 16 2 Primitives for networking sais cce 6 bs he ee oP eee Program examples bil Draw houses 242 458 4 5 446 a4 64 85 4 eke ada ROS AGES a we E 5 2 Draw a whole rectangle ka ea a a a koa GOR a O arn D3 Factorial dit E a a deeb e PG ee ee hoe we ews Sa R e A 5 4 The snowflake with thanks to Georges No l oD A little Pt Of writin e derer e e a be doe bee ek ee ER a Go E Se A D0 And conjugation lemas ata a a a E ae aa a a a E Dat A s e e ake e a om ond a ai a eh a ak E a e lar E ee E 5 8 gt SeCOnd PO a a e bee os ee S a a A A we ae D ee De a ee 5 9 Oreven A little recu
41. since the start of program execution readchar e If key is false the program is paused until the user presses a key e If key is true it gives the key which was pressed last These are the values given for particular keys A gt 65 B gt 66 C gt 67 etc Z gt 90 gt 37 or 226 NumPad Tf gt 38 or 224 gt 39 or 227 gt 40 or 225 Echap gt 27 F1 gt 112 F2 gt 113 sets F12 gt 123 Shift gt 16 Espace gt 32 Ctrl gt 17 Enter gt 10 Table 4 1 Values for particular keys If you are uncertain about the value returned by a key you can type pr readchar The interpreter will then wait for you to type on a key before giving you the corre sponding value read List title word Presents a dialogue box whose title is list_title The user can then input a response in a text field and the response will be stored in the form of a list in the variable word and will be evaluated when the OK button is pressed 4 14 2 Some examples of usage to vintage read What is your age age make age first age if age lt 18 pr you are a minor if or age 18 age gt 18 pr you are an adult if age gt 99 pr Respect is due end to rallye if key make car readchar if car 37 lt 90 if car 39 rt 90 if car 38 fd 10 if car 40 bk 10 if car 27 stop 35 rallye end You can control the turtle with the keyboa
42. t for the use of files To set your current directory path to c My Documents setdir c My Documents Please note the use of to notify the space between My and Documents If you forget the double backclash the path that will be defined will then be c My Documents and the interpretor will send you an error message 3 4 Case sensitivity XLOGO makes no distinctions on case as regards procedure names and primitives Thus with the procedure square as defined earlier whether you type SQUARE or sQuaRe the command interpreter will translate it correctly and execute square On the other hand XLOGO is case sensitive on lists and words print Hello gt Hello the initial capital H is retained 3 5 Operators and syntax There are two ways to write certain commands For example to add 4 and 7 there are two possibili ties you can either use the primitive somme which expects two arguments somme 4 7 or you can use the operator 4 7 Both have the same effect This table shows the relationship between operators and primitives m ees ee ALT GR 7 The two operators and amp are specific to XLOGO They do not exist in traditional versions of LOGO Here are some examples of usage pr 3 4 7 1 gt true pr 3 4 7 49 7 gt true pr 3 4 amp 7 49 7 gt false 10 3 6 A word on colors Colors are defined in XLogo with a list of three numbers r g b between 0 and 255 The number r is the red compone
43. to the clipboard Edit gt Cut cut the selected text to the clipboard Edit gt Paste paste the text contained in the clipboard into the command line Options Menu Options gt Choose the pen colour allows the colour with which the turtle will write to be chosen from a palette of colours Also accessible via the command fcc Options gt Choose the background colour set the colour of the screen background Accessible via the primitive fcfg e Options gt Define start up files allows the path to start up files to be defined Any procedures contained in these lgo format files will then become pseudo primitives in the XLogo language They cannot be edited or changed by the user You can thus define personalised primitives e Options gt Translate source Allows to translate source from a language to another In fact very usefull when you want to use for example downloaded Logo source written in another language e Options gt Preferences opens a dialog box in which you can configure several things 2 4 Language allows French Spanish or English to be chosen Note that the primitives differ in each language Look allows the look of the XLogo window to be defined The Windows native Java and Motif styles are available Choose the drawing speed If you prefer to see all the turtle s movements you can slow it down by using the slider bar on the first tab On the
44. with the primitive print or write setseparation setsep This table sets out the primitives which allow the properties of the text area to be adjusted Those primitive that control the color and the size of the history area are available only for the primitives print or write 15 Primitives Utilisation none Empties the area containing the command and com ct cleartext ment history word list or shows the argument specified in the history zone pr print number pr word list or The same as for the print primitive but doesn t go number back to the line a number Define the size of the font in the command history sit Only valid with the primtive print setfonttext none Returns the size of the font with primitive print ftext fonttext a number or Define the color of the font in command history Valid SCl list only with the primitive See p 11 setcolortext none Returns the color of the font with the primitive print ELSE in the command history colortext n number Select the font number n when you write on the the set nt command history with the primitive print You can setfontnametext find the link between number and font in Menu gt Options gt Preferences gt Tab Font none Returns a list with two elements The first is the num fnt ber corresponding to the font used when you write on fontnametext the command history with the primitive print The last element is a list which contains th
45. word a list or an already defined procedure e Lists These are defined between brackets Numbers are treated in some instances as a numeric value eg fd 100 and in others as a word eg print empty 12 writes false 3 2 Procedures In addition to these primitives you can define your own commands These are called procedures Procedures are introduced by the word to and conclude with the word end They can be created using the internal XLOGO procedure editor Here is a small example to square repeat 4 forward 100 right 90 end These procedures can take advantage of arguments as well To do that variables are used A variable is a word to which a value can be assigned Here is a very simple example to twice word print word print word end twice 1 2 3 gt 123 See the various examples of procedures at the end of the manual 3 3 Specific character The specific character backlash especially allows the creation of words containing blank or line feed symbols If An is used the phrase skips to the following line and followed by a blank means a blank in a word Example pr xlogo xlogo xlogo xlogo pr xlogo nxlogo xlogo xlogo You can therefore only write the symbol by typing Same behaviour characters are specific delimiters of Logo If you want to use them in a word you just have to add the character before All only symbols are ignored This remark is especially importan
46. xt from the clipboard IMPORTANT e Note that clicking on the close button x in the window titlebar will have no effect Only the two main buttons will allow you to quit the editor e To delete one or more unwanted procedures use the primitives er and erall Chapter 2 Menu options 2 1 2 2 File Menu File gt New Delete all procedures and variables You create a new workspace File gt Open open a previously saved logo file File gt Save save the procedures in the current file File gt Save as save the current procedures under a specific name File gt Quit quit the XLOGO application File gt Capture image gt Save image as allow the image to be saved in the jpg or png format If you wish to select only a part of the image you can define a bounding box by cicking twice in succession to define the two corners of a diagonal through the bounding box File gt Capture image gt Print image allows the image to be printed In the same way as above you can select an area to print File gt Capture image gt Copy image into the clipboard Put the image into the system clip board Just as for prinitng and recording you can select a zone of the image This functionality works very well under the Window environments On the other hand it does not work under Linux the clipboard have a different behaviour Untested under Mac Edit Menu Edit gt Copy copy the selected text
47. y the second the month and the last the year gt day month year eons aucun Returns a list of three integers representing the time The first integer indicates the hour the second the minutes and the last the seconds gt hour minute seconde i none Returns the past time in seconds since XLOGO has pasttime sorted Difference between wait and countdown is that countdown doesn t halt the program Here is an example to clock shows time in numerical format we refresh the time each five seconds if endcountdown cs sfont 75 ht make heu time make h first heu make m item 2 heu We shows two number for seconds and minutes we must add a 0 if m 10 lt 0 make m word O m make s last heu We shows two number for seconds and minutes we must add a 0 if s 10 lt 0 make s word O sl label word word word word h m s countdown 5 clock end 39 4 16 Using a network with XLogo 4 16 1 The network Howto First we have to introduce the basis for network communication before we can use the XLogo primi tives Two computers or more can communicate through a network if they both have ethernet cards Ko Address 192 168 1 1 Address 1927 168 1 2 Name hare Name turtle Figure 4 5 A simple network Each computer is identified by a personal address called an IP address This IP address consists of four integers each between 0 and 255 and separated by a dot For example The
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