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1. Scr 1763 0 deskjet dj 9 1 FORTH DEFINITIONS 4 88 CRC 11 35 2 DJ BL WORD HERE COUNT UPPER and away we go 3 HERE DESKJET C gt P LITERAL F FIND 0 0 ERROR Because string construc 4 STATE F lt IF lt COMP gt ELSE EXECUTE THEN tion is from right to left the 5 IMMEDIATE Ss end of command character 1 6 Allows instant access to a deskjet word the right hand one in the stack 7 It finds the word in the deskjet vocabulary and either diagram char3 and the cat 8 compiles it or executes it according to its immediate egory character is on the left 9 bit and the contents of STATE charl This makes for very 10 N B Will also find words in the FORTH vocabulary readable code as illustrated 11 This is a specific version of Brad Rodriguez FROM which by POINTS on line seven of 12 is used to get a word from a designated vocabulary e g the same screen The charac 43 FROM EDITOR TEXT ters are simply in the reverse 44 Instead use it as follows order of their positions inthe 45 DJ BOLD ae DJ BOLD output string In the case of the points command the syn tax is lt esc gt s V for the oor 1780 primary font 0 deskjet c 2 20 10 88 CRC 15 55 The defining word POINTER lets the user define point sizes he might wish to 3 use routinely Alternatively he 4 can use POINTS to command 5 oddball point sizes subject to 6 7 8 9 2 TASK the printer s limitations
2. 1 DESKJET FORTH DEFINITIONS C 2 PRINT OUTFILE OR IF DESKJET 5PITCH ASCII C EMIT 10PITCH SUPERSCRIPT 6POINT ASCII 2 EMIT 12POINT SCRIPT FORGET TASK BASE DECIMAL gt R print c 2 logo on deskjet ELSE C 2 THEN On screen 1757 we make arrangements to allow a con TASK sistentunderline style through 49 p gt BASE EDITOR FLUSH out a document The printer 44 syntax is to have to set the 45 underline type each time the 43 user wants to add underlin 14 ing This requiresthatthe user 15 remember which flavor of underlining he wants Instead we remember it for him with the variable UNDER Daughter words of the defining word LINER allow the user to specify his preference for underline style and the words UNDER LINE and UL turn underlining on and off respectively The next several screens are straight definitions of various PCL commands On screen 1762 we handle the need to track our position on the paper during printing This capability allows applica tions to stop printing a document print footers go to the next page print headers and then resume printing the document It also allows an application to force text onto the next page in order to preserve a section intact It also allows proper handling of footnotes The key to a Deskjet carriage return is to move the printer vertically with the word gt VERTICAL followed by paging if necessary and then moving the carriage to
3. DADA UO AUNE deskjet font designators 1752 FSEQ PC 8 10U FSEQ ROMAN8 8U FSEQ PC 8DENMARK 110 FSEQ LATIN1 ON FSEQ ISO UK 1E FSEQ ASCIIO6 0U FSEQ ASCII14 0K Scr 0 deskjet font designators 1753 1 FSEQ COURIER s3T 2 FSEQ CGTIMES s4101T 3 4 5 6 7 8 9 10 11 12 13 14 15 PRIMARY PRINT IF CTL O shift SE CONDARY SECOND ON 9 4 88 CRC 9 58 21 2 93 CRC 17 35 SECOND OFF select primary font in EMIT THEN select secondary font PRINT IF CTL N shift out EMIT THEN Scr O deskjet subscripts italics bold 1 FSEQ FSEQ FSEQ FSEQ FSEQ FSEQ FSEQ FSEQ FSEQ 1754 SUBSCRIPT s 10 SCRIPT s0U SUPERSCRIPT S1U PROPORTIONAL s1P FIXED s0P ITALIC s1585 ITALIC S0S BOLD s3B BOLD s0B fastForth on Atari ST Mond ay 8 3 93 10 12 56 23 2 93 CRC 10 44 ITALIC ITALIC ITAL ON ITALIC ITALIC ITAL OFF BOLD BOLD BLD ON BOLD BOLD BLD OFF c 1985 92 by Charles Curley 30 Forth Dimensions Scr 1755 0 deskjet character height 23 2 93 CRC 11 39 1 BUILDCMD n chrl chr2 ch3 string typed 2 OUT F gt R PRINT IF LI EMIT THEN BASE F gt R DECIMAL 3 gt R gt R gt R DUP S gt D DABS 4 lt R gt HOLD S DJSIGN R gt HOLD R gt HOLD gt 5 TYPE R gt BASE F P gt OUT F 6 7 POINTS pts set font height i
4. eeeoeoeoeoeoe Forth Dimensions ofan inch high superscript The superscript 2 is then printed We then return to our normal 12 point text Then we restore printing from the superscript line to the base line Further Enhancements One thing not done here is to track more variables The driver could track and make available to the application the current horizontal position Cin say decipoints the current pitch and point size and other variables One of the problems with the application word C 2 is that it leaves the printer in 12 point and 10 pitch Point and pitch could have been saved going in and then restored at the end Horizontal movement is dealt with crudely all type is assumed to be monotype This is fine for the Courier typeface but doesn t work in CG Times a proportional typeface A proportional typeface might require some look ahead to determine where to break lines To get right justification we would have to add a variable to hold padding values for characters and word gaps Another thing not implemented here is cursor movement Vertical movement is present in 48ths of an inch increments A re write to give decipoint and character cursor movement would make multi column printing and precise placement of graphics from a word processor very easy Availability The code shown here is released to the public domain Enjoy it in good health and raise a toast to those who contribute to the public domain from t
5. 0 SWAP c num Clean up the output of the loop double addr sign successf double true false IF SWAP DROP IF DMINUS THEN 1 ELSE 2DROP 2DROP 0 THEN Forth Dimensions 13 July 1993 August FORTH DEFINITIONS 2NUMBER The actual word addr of number double true false HIDDEN s num gt R BEGIN wt num WHILE wl num REPEAT R gt SWAP c num FORTH S scr 15 Extensions to 04 23 93 C Character plus store val addr SWAP OVER C SWAP C I OR store val addr SWAP OVER OR SWAP CI Character OR store val addr SWAP OVER C OR SWAP C amp AND store val addr SWAP OVER AND SWAP C amp Character AND store val addr SWAP OVER C AND SWAP C XOR store val addr SWAP OVER XOR SWAP C Character XOR store val addr SWAP OVER C XOR SWAP C gt scr 16 Extensions to 04 23 93 Minus store val addr DUP ROT SWAP C Character minus store val addr DUP C ROT SWAP 7s scr 17 CELL MOD 04 23 93 Faster than CELL MOD CELL MOD Divide the value on the top of the stack by the cell size leave remainder val rem quot DUP 1 AND SWAP 2 On a 32 bit machine this would be CELL MOD DUP 3 AND SWAP CELL 7S ADVERTISERS INDEX AM Research s cascsd
6. definition of prepositions and special words such as of from into is and the is explained in the next section Prepositions and Other Keywords Most of natOOF s special features are based on OOF s multiple polymorphism interpret makes a lot of deci sions based on the classes of objects that are passed as arguments for a method which in most other languages the programmer has to do himself in the form of if e1se or case clauses or with extensive use of flags natOOF uses keywords to differentiate between methods of the same name and arguments Keywords are just normal objects if of special classes Prepositions such as from into of onto under etc are implemented as objects of the classes _from _into _of _onto _under etc respectively They can be used e g in readWord into Inword from Instream where they have no function except to make the sentence July 1993 August Im interpret if EndofSentence EndofSentence FALSE if the Verb is empty readWord into Inword from Instream else Inword endif else readWord into Inword from Instream endif Verb if OOF_COMPILE Figure Three natOOF s interpret written in natOOF OSAT TEE define method interpret stream Instream input output input output and local ob string Inword Verb local objects jects ofa method Classically a global state flag is used EndOfSentence FALSE which a single would test
7. platforms More recently Federal Express has been maintaining two major Forth based systems the oldest of which dates from 1987 They have a team of about eight programmers who maintain both these and some C based systems They have told us they find the Forth based systems far easier to maintain than the C based systems they can tum change requests into releases in only a few weeks rather Forth Dimensions than months It is specious to equate using Forth in a shop that may also use C to 22 dialects of 13 programming languages 2 Choice of language doesn t matter agree that it often seems that way to most managers and programmers as well In regard to choosing say C vs C or Pascal it s probably even accurate But choosing Forth can often reduce costs as well as calendar time which is often more important by really significant margins Not only can the work go quicker with a smaller programming team it frequently also requires much simpler cheaper comput ers to run on When we developed the Heating Ventilation and Air Conditioning HVAC system for the GM Saturn plant in Tennessee they told us we saved them several million dollars over more conventional approaches We did this by developing software that ran on cheap embedded Z 80 boards coordinated by a few PCs rather than using many VAXs as proposed by the next lowest bidder On the Saudi Arabian airport project in the mid 1980 s we pr
8. several blocks Fortunately as Forth programmers we are in control of our environment so can anticipate the effects of how our data is organized How significant this effect is will vary from Forth to Forth depending on how many block buffers there are and what algorithm is used to decide which buffer is written to next In my case I have a measly single block buffer which is probably the worst of all possible setups but given one meg of flat RAM I seldom use the disk for anything other than saving data at the end of a session Those who endure a segmented memory may wish to consider modifying BLOCK so that a range of block numbers refers to chunks of extended memory rather than to disk sectors This seems a simple way of adapting to an inconve nient architecture There is no reason that the virtual dictionary could not contain executable code as well as data However this tends to be non portable and requires as a minimum the facility to produce headerless words This means that it is rather beyond the scope of this article so I simply mention it as a possibility July 1993 August Error Handling The code published here does not contain error handling routines This is not idleness it is a design decision This decision is made for several reasons which I will mention in no particular order Firstly in published code it distracts from the intention of the article Secondly error handling routines serve two distinct purpos
9. Covers all aspects of using an 80386 microprocessor By Penn and Don Brumm 386sx Microprocessor Programmer s Reference Manual Basically what the title says Published by Intel EGA VGA A Programmer s Reference Guide Used as a reference in the article about character device drivers By Bradley Kliewer AT BIOS KIT The Comprehensive Guide to Creating an AT BIOS in C Used as models for the device drivers By John O Foster and John P Choisser published by Annabooks 12145 Alta Carmel Ct Suite 250 San Diego California 92128 Operating Systems An overview of OS functions and design issues By H M Deitel scr 10 Basic tools 04 09 93 BASE DECIMAL comment to end of line BLK IF IN 64 OVER OVER MOD SWAP ELSE 0 DUP TIB IN THEN IMMEDIATE Now the word will comment to the end of a line either interpreting from a block file or the terminal Notes this will not work on a FORTH 83 system This implementation has a misfeature if the word is interpreted at the exact end of a line in a block it will skip the entire next line This is left in because the code to catch the special case would be warty July 1993 August 12 Forth Dimensions scr 11 Basic tools 04 09 93 AUTOLOAD autoload a dependant word from a block block FIND IF DROP 2DROP ELSE LOAD THEN Used in this idiom gt 27 AUTOLOAD FOO will load screen 27 if the word FOO is
10. Jack s we have made strenuous efforts to make requirements clear If they are not clear we would greatly appreciate knowing what is confus ing so we can clarify it But such comments are useful only in reference to a particular draft preferably the current one Consider the example that Curley raises the definition LEMME OUT 100000 0 DO I 1000 IF LEAVE THEN I LOOP In the first place a point Curley misses although this may compile fine on Vesta s 68332 32 bit Forth the standard does not guarantee that the literal 100000 will compile correctly on 16 bit systems The phrase ENVIRONMENT MAX N will return the value of the largest usable signed integer on a particular system Moving on to the points he does raise I wonder why he thinks it might not compile He seems to be concerned about the control flow stack however for each word that has prescribed compile time behavior use of the control flow stack is explicitly documented In this example the affected Forth Dimensions so we can avoid revisiting problems we ve already solved _ words show their compile time stack behavior as DO CC do sys IF C orig THEN CC orig LOOP CC do sys No other words including I and LEAVE have any compile time action or affect the control flow stack which exists only at compile time in any way Therefore if the structures are nested properly they are the definition will compile properly No c
11. Jim has provided details of his own rites of passage Discerning readers will notice congruities between Jim s article and Mike Elola s essay in this installment of Fast Forthward I m tempted to ponder whether this represents Forth s future But itis probably more accurate to observe that this is another of the faces that Forth s extensibility malleability permits it Whether its virtue suffers or is lost entirely in the translation will depend on both the eye of the beholder and the mind of the implementor Marlin Ouverson July 1993 August 4 Forth Dimensions Volume XV Number 2 July 1993 August Published by the Forth Interest Group Editor Marlin Quverson Circulation Order Desk Frank Hall Forth Dimensions welcomes editorial material letters to the edi tor and comments from its readers No responsibility is assumed for accuracy of submissions Subscription to Forth Dimensions is included with membership in the Forth Interest Group at 40 per year 52 overseas air For mem bership change of address and to submit items for publication the address is Forth Interest Group P O Box 2154 Oakland California 94621 Administrative offices 510 89 FORTH Fax 510 535 1295 Advertising sales 805 946 2272 Copyright 1993 by Forth In terest Group Inc The material con tained in this periodical but not the code is copyrighted by the individual authors of the articles and by Forth Interes
12. S V P R S V P Russell Harris is an independent consultant providing engineering program ming and technical documentation services to a variety of industrial clients His main interests lie in writing and teaching and in working with embedded systems in the fields of instrumentation and machine control He can be reached by phone at 713 461 1618 by facsimile at 713 461 0081 by mail at 8609 Cedardale Dr Houston Texas 77055 or on GEnie address RUSSELL H July 1993 August Fast Forthward continued from page 37 face for Computing Standards Once those and the other POSIX services have been shown to be robust and efficient when generated from Forth Forth can more readily support the many applications that are part of UNIX Furthermore it would be a first step towards open systems compliance These POSIX conformant routines should be incorporated into Forth through a linker s editing of previously compiled relocatable object modules Besides following the industry standard for layering software regard less of its source this would help encourage the POSIX work to be reused across Forth platforms and would encourage Forth implementations to be more conversant with linkers Forth source code for POSIX routines would also support code reuse but only if Forth systems have suitable and standard routines for implementation of specific POSIX services This is not currently possible for services such as process man
13. This word is used primarily to determine the number of cells an object will occupy CELL MOD n rem quot An alias for CELL MOD Depending upon the implemen tation can be faster than the actual code fragment For example ona 16 bit system this can be implemented as DUP 1 AND SWAP 2 which is faster because 2 is implemented as a shift and not a true divide CELLS n n The constant value CELL is multiplied by the value on the top of the stack Used to determine the number of address units occupied by a multi cell object or to access a field n cells from the beginning of a record c val addr Logically XOR the character value val with the value at addr CI val addr Logically OR the character value val with the value at addr A val addr The value val is logically XORed with the value at addr c num double addr sign flag double true false Cleans up the output of NUMBER s num addr double 0 addr 1 true sign flag Sets up the BEGIN WHILE REPEAT loop of NUMBER wl num double addr double addr decimal place flag The WHILE loop portion of NUMBBER wt num double addr decimal place flag double addr true double addr true false false The WHILE test portion of NUMBER val addr The value val is logically ORed with the value at addr July 1993 August Bibliograph
14. and Linda Baker and surprisingly still available from Mountain View Press Forth Dimensions vols 1 12 A forum for exploring things Forth Several volumes are out of print American National Standard for Information Systems Program ming Language C Used as a reference in the articles about translating C to Forth The C Programming Language The standard reference for the C programmer Used primarily for its description of the C language in the C to Forth compiler and for the heap management functions found in the last few chapters SCO XENIX System V Release 2 3 2 Programmer s Reference Manual and Guides The documentation provided with the SCO XENIX development system now in release 4 The description of the Intel relocatable object module format is used as a model for the design of relocatable Forth object modules The programmer s guides entries are used for the descriptions of the XENIX UN X utilities used in the project lex and yacc A tutorial on the complementary UN X utilities dex and yacc A nutshell handbook by O Reilly and Associates Compilers Principles Techniques and Tools The second edition of the Dragon Book A very dense basic reference on all aspects of compiler theory from lexical analysis and parsing to sophisticated optimization strategies By Alfred Aho Ravi Sethi and Jeffrey Ullman names that figure prominently in the history of UN X 80386 A Programming and Design Handbook
15. be fairly well versed in UN X like operating systems after about three years of interaction with them and 120 hours of instruction Recently started looking into C a language in which expectto receive an additional 120 hours of instruction and in which I ll probably be somewhat less than competent For those of you interested in why have such diverse exposure have only my father to blame thank pick one For several years my father would find a really neat way of doing something programming a computer selecting music what have you and run straight out to tell someone Since lived with him at the time was something of a captive audience He would go straight to me interrupt whatever was doing and tell me all about the neat little trick he d discovered Since was usually playing Caverns of Mars or doing something equally as important resented the interruptions However he persevered in his quest and showed me what STAR ASCII EMIT did When replied That s nice but what else can it do he handed me a copy of Leo Brodie s Starting Forth and told me to go to it promptly put the book away and went back to playing Caverns of Mars This was during the summer spent more time at the computer than would spend in my state mandated secondary school classes for the next three years One day during the same summer after I d spent all morning trying to figure out how to get the compute
16. of an inch to achieve six lines per inch so LNED is initialized to eight at compile time On lines four and five we define a word to allow us to follow which font is active the primary or the secondary Commands to the two fonts are differentiated by the pres ence of a left or right paren thesis in the command so FONT returns the appropri ate character Note that this works because ofa peculiarity of the ASCII character set Those using EBCDIC or other character sets may have to re write this word as well as provide a translation table from their character set to ASCII for the printer s benefit There are some commands which insist on an embedded plus sign The Forth word SIGN is used to insert a minus sign into a string indicating a negative value However it inserts nothing into a string if the value is positive Hence we provide the word DJSIGN on line eight On the next screen we write two defining words for sending sequences of charac ters to the current output de vice In both cases we compile a string in line to be sent to the output device At run time the code examines the current output device with 7PRINT to see if it is the printer If it is we send the escape character otherwise we do not send it This allows us to debug by printing to the screen The difference between the two defining words is this FSEQ is used to send font command sequences These July 1993 August Ser 0
17. psychologists on our interdiscipli nary research team A step towards usability and acceptance of an application language is to make the programming style resemble the natural language of the programmer as much This enables non experts to concentrate on a solution rather than on a computing syntax as possible natOOF offers a first step in this direction to overcome the described restrictions It was designed to enable non experts to program their application in a style that is close to their natural language so they can concentrate on their solution rather than on the syntax of a computer language This shall be supported in as many mother tongues as possible since this is the language we all speak best The base is the object oriented Forth OOF which was introduced in issue XIV 1 of Forth Dimensions in 1992 Here is a short recap of its essential features e It provides Forth s interactivity and extensibility and the possibility to tailor an application language free of any syntactical constraints It is enhanced with features of object oriented languages such as a hierarchical structure of classes and methods Forth Dimensions Natural Language Programming First steps towards programming in natural language style in the object oriented Forth natOOF inheritance and multiple polymorphism plus the security of strong typing These main buzzwords of object oriented languages are explained briefly below
18. return stack is returned by the word I a copy of the second item on the return stack is returned by the word J Your Pad or Mine The pad scratch pad is of indeterminate size and is located at a fixed offset from the top of the dictionary Thus the pad resides in the region between the parameter stack which grows downward and the dictionary which grows upward The region between the pad and the dictionary is used for formatted numeric output conversion The address of the pad is returned by the word PAD which is defined in terms of the dictionary pointer H Continued July 1993 August Necessary Appurtenances In order to metacompile at least two additional pointers are required Obviously we need a dictionary pointer for the future application dictionary which will reside in read only memory ROM Additionally during compilation we need a pointer for the future application read write memory RAM so we can assign RAM for application variables arrays etc and for system functions stacks buffers etc Curiously it is not necessary to have a pointer for the virtual application dictionary which is being built within the development system hardware the physical addresses within the development system can be computed on the fly from the corresponding addresses in the future application dictio nary We need words to set to advance and to read each of the application pointers We also need a word to transfo
19. string and the string TYPEd to the current output device On line two we save two variables to the return stack OUT is used to count text output in a line These commands should be transparent to text output so we fake it by preserving its contents for restoration on line five Similarly we must be in decimal regardless of the current base On the same line if the current output device is the printer we emit an escape to indicate the start of a command On line three we save the three characters to the return stack This is to allow the code to manipulate the numeric argument which we do immediately The DUP places a copy of the number on the stack The lower copy will be used by DJSIGN at the end of numeric conversion The upper copy is sign extended to a double precision value and converted to an absolute value ready for numeric conversion Line four begins string construction The phrase R gt HOLD adds character one to the string under construction 5 then converts the number value to a string leaving a double precision 0 on the stack to be removed by gt later DJSIGN is executed in order to force either a plus or a minus sign into the string Twice more we execute the phrase R gt HOLD to add the remaining two characters to the string gt consumes the July 1993 August double precision 0 and leaves the address and count of the string ready for TYPE on line five We then restore our vari ables from the return stack
20. takes to place the verb somewhere within the sentence Forth Dimensions 19 nated by a semicolon it is tedious and a source of errors So by default a sentence is terminated at the end of the line In this case lt CR gt is read from the input stream and a word of that name is executed which sets EndOfSentence to True On the other hand the characters extend the sentence to the next line if necessary If the verb is not found after the sentence is finished an error message is displayed and the interpretation is termi nated The same reaction takes place if one of the nouns or prepositions of the sentence is not found This strategy is illustrated in Figure Three by the code of natOOF s interpret which is written in natOOF itself to demonstrate its use The example also shows how to define a method by supplying its name the input parameters the output parameters and local objects The syntax input output local is derived from Forth s stack comment before after Note that all objects are typed they are defined as objects of a class The colon definition was generalized to define objects of any class in the format classname objectname For a detailed description see Forth Dimensions May June 1992 or the euroFORML 91 Proceedings for the paper describing the object oriented Forth OOF The assignment statement has now become the verb which is explained later The implementation use and
21. the attention of the FD editor For some of the suggested topics see the FORML announcement on the back cover contest details are provided in the ad on page six of our last issue Our last issue carried Donald Kenney s Forth in Search of a Job The author gave reasons why a software manager might reject Forth as a programming solution in a corporate environment The objections sounded familiar and a little depressing perhaps even reasonable from a certain point of view Were they blunt words a death knell or a healthy dose of reality therapy Well old hands at the sales game know that once you have a clear picture of a prospective customer s objections you are on the road to making a sale Elizabeth Rather President of Forth Inc and chairperson of the committee developing ANS Forth responds in this issue with a letter I d like every Forth programmer and business to carry prominently in their consciousness After twenty years of running a leading Forth business Ms Rather has heard all the arguments against Forth and has an impressive arsenal of evidence and case histories with which to shoot down each of those objections We are fortunate to have her no nonsense attitude and get the job done approach in our community It seems to me that as always we have choices about how we react to the world We can beat our breasts and whine about Forth s market share or we can use our assets to penetrate and impress the portion
22. the last character is sent upper case For example the three commands lt esc gt s3T lt esc gt s3B and lt esc gt s2Q may be combined into one command lt esc gt s3b3t2Q Note that the periods and commas are punctuation not part of the commands This facility can be used to build custom printer commands This suggests that the key to H P PCL is a sequence of numbers values of some sort followed by letters which indicate commands Hmm value command value com mand Sure sounds familiar to me Somehow I don t think we re in BASIC any more Toto Two control character commands select the primary and secondary fonts This means that two fonts may be defined once in a document and the user may select between them merely by issuing either lt si gt or lt so gt This is useful if one wishes to switch between two different fonts For example one might write an article on H P Deskjet drivers with the text in proportional CG Times 12 pitch and the sample code in Forth Dimensions Scr 1749 0 load deskjet printer driver _ FILING FORTH DEFINITIONS FORGET TASK VOCABULARY DESKJET IMMEDIATE DESKJET DEFINITIONS 9 4 88 CRC task BASE F gt R DECIMAL 1 14 THRU O eenn HB WN FE Pe H FORTH DEFINITIONS R gt BASE f EDITOR FLUSH TASK Hrem U wN Scr 1750 variables deskjet printer driver VARIABLE SECOND VARIABLE BLD VARIABLE ITAL 8 VARIABLE LNFD HERE 0 CONSTANT
23. the sentence Example next Buffer read into it from Instream does the same as read into next Buffer from Instream in the example above it can therefore be used to separate sentences without stackrobatics such as swap or rot it changes the order of the stack entries by moving not copying the referred object to TOS e An object in OOF may consist of other objects E g a string object contains the maximum length max the actual length length and the text of the string text These may be accessed only in methods for strings a feature called data encapsulation The actual length of the string name is accessed by name gt length In natOOF s does exactly the same as gt but looks more natural name s length Extended and Unified Loop Structure The object oriented nature of natOOF especially its multiple polymorphism feature makes it possible to redefine the loop control structure such that the programmer always uses the same set of control words regardless of the kind of loop The idea here is to make looping structures more readable and easier to write Incidentally this concept was triggered by Gordon Charleton s talk on this topic at euroFORTH in October 1992 in Southampton Englad see also his article One Screen Unified Control Structures in Forth Dimensions X1V 6 The basic frame of a loop is repeat sentences end which is an endless loop The sentences remember natOOF slang for
24. they are in fact identical but for one word which in the case of V needs to be UPDATEd and for VR needs to be SWAPped Such an unusual circumstance requires unusual factoring particularly since it is in the middle of a control structure and as I require good access to four stack items it is optimal to keep some on the return stack The route I chose was to effectively patch V during execution using the execution vector FIX which has either UPDATE or SWAP assigned to it as required V takes three parameters a source address a virtual destination address and a length in bytes of the data to be stored in virtual memory It then divides the length into handy bite sized pieces to MOVE into the block buffer With a large structure the first and last pieces may not be exactly 1K long so the first line of code after the WHILE calculates the correct length for each piece The next line does the MOVE the third increments the source and destination addresses by the size of the piece that was MOVEd and the fourth line decrements the remaining length by a similar Forth Dimensions amount Ideally this would have been done inside a DO LOOP except for certain problems with Forth s counted loops To be specific V is best coded with the length as the loop index This implies a negative going loop Furthermore it should be reasonable to pass a length of zero as an argument which implies a zero tripping loop Unfortunately ze
25. tools I ve built over the years Some of the tools will be used in the articles and some won t be The tools that I m not using in the articles are there because I m an irrepressible tool builder and I like to have complete symmetrical sets of related tools sets I call orthogonal the only reason for the existence of C etc in my toolkit One toolset in particular is a ktudge I used trying to manage large libraries of source code and not very successfully since it relies on absolute block addresses and I move source code fairly freely By the way I use the UN X convention of letting the vertical bar stand for or in a list of choices Thus if a Forth word could return a value and a true flag ora false flag I would diagram its stack effect like val true false and if it left either a value or zero I would diagram it like val 0 Enjoy July 1993 August About Jim Schneider it has been pointed out to me that some may find my background interesting Well you asked for it Marlin lve been programming in Forth for about ten years now and programming in C for about eight consider myself to be an expert in both i e if were given sufficient time and motivation could write a compiler for either find it noteworthy that achieved expert status in Forth without benefit of formal instruction but I ve taken 18 weeks 120 hours of classes on C also consider myself to
26. value on the stack F is a fast word boundary only version of as F is a fast word aligned version of Users of other Forths will have to adjust the code ASCII control characters hex 0 to 1f will be indicated by name in brackets lt esc gt lt lf gt etc Background Hewlett Packard has offered the PCL printer control language in their laser printers for some years The H P Deskjet series offers less expensive inkjet technology with much the same printer control language Although the PCL language is very flexible drivers for it can be implemented in Forth readily H P PCL PCL comes in various levels The higher the level number the more recent and generally the more extensive the abilities of the printer Each level is supposed to be a proper superset of the previous level The generic PCL command string is begun with an escape character hex 1b or lt esc gt This is followed with a punctuation character which indicates a broad category of the command Commands which control the printer in general are indicated by the ampersand amp character These include the nature of the underscore to be used the page orientation margins etc Font characteristic commands are indicated by the left paren thesis for the primary character set and by the right parenthesis for the secondary character set These commands influence such things as bold italic point and pitch Graphics and font download commands are indicat
27. with speeds and headings programmers deal with quantities of data and directions of increment Addressing the Matter of Pointers Forth is a language of pointers In the following para graphs by pointer I mean simply a register or a memory location which holds an address However it is not uncom mon to see the word pointer used for the address itself Context usually makes clear the usage The pointer of which most programmers are first aware is the dictionary pointer H which holds the address of the next available byte in the dictionary of the development system The value in H is returned by the word HERE The virtual Forth machine is based upon a set of pointers which are as follows U the user pointer holds the base address for user variables for the current user i e task S the parameter stack pointer R the return stack pointer I the address interpreter pointer holds the address of the code field of the next word to be executed W the address interpreter word pointer holds upon entry to executable code the address of the param eter field of the word being executed Although variables are frequently used for pointers this particular group of pointers is typically implemented in processor registers in order to minimize access time and thus maximize speed of the Forth machine Note that the address Continues on page 41 July 1993 August CALL FOR PAPERS for the fifteenth annual and the 1993 FORML CONFERE
28. 0761 Oo Forth Dimensions FIG FORTH Jim Schneider Sunnyvale California This series of articles is my attempt to give back something to a language and a culture that has given so much to me Essentially I m attempting to build a development environ ment that has the advantages of both Forth and UN X and hopefully sidesteps the disadvantages In my opinion the use of Forth as a mainstream language is hampered by the fact that programmers not accustomed to the Forth philosophy are loath to give up the tools with which they are comfortable long enough to learn how to be productive in Forth Additionally some of Forth s best tools are very difficult to learn and even harder to modify Furthermore there is Forth s perennial standards debate various gross and subtle inconsistencies between different implementations of the same standard and a lack of some tools thata UN X programmer would take for granted When these points are taken altogether Forth appears more and more limited I hasten to add that this is not to say that Forth has to be limited or limiting but that Forth doesn t have the tools integrated into it that most non Forth programmers expect in a development environment My number one priority is merging the capabilities and strengths of Forth and UN X These observations lead me to an inevitable conclusion the most extensible in some senses the only extensible computer language in the world needs to b
29. 32 Parallel Coprocessor Sys 32 bit SC32 industrial grade Forth PGA CPU System speed options 8 or 10 MHz 64 KB to 1 MB O wait state static RAM Full length PC XT AT plug in 6 layer board SC FOX SBC Single Board Computer RTX 2000 industrial grade PGA CPU System speed options 8 10 or 12 MHz 32 KB to 512 KB O wait state static RAM 100mm x 160mm Eurocard size 4 layer board For additional product information and OEM pricing please contact us at SILICON COMPOSERS INC 208 California Avenue Palo Alto CA 94306 415 322 8763 COntentsS Features 9 The FSAT Project Jim Schneider A development environment with the advantages of both Forth and Unix would include the tools which many mainstream programmers are comfortable with and which they have come to expect It would also offer access to Forth by those who otherwise might not tread its alien to C users territory Not incidentally it would provide new tools to Forth programmers Part one of a series Forth follows the assembler paradigm data is not typed the programmer must keep track of it on the stack And because operators are not overloaded different functions must be specified for the different data types The author shares his pre defined functions the better to use public domain source code that may require such routines 1 5 Mixed Integer Arithmetic Walter J Rottenkolber 1 7 Towards Natural Language Programming Markus Dahm Forth is o
30. COMPILE state So the only thing missing is a way to determine the end of d methods for object on TOS if any global objects globa words literal number char or string global objects global words local objects and parameters methods for object on TOS if any literal number char or string the sentence One way is to end it explicitly with a period which sets EndOfSentence to True Although this is close to other computer languages where a statement is termi number of objects where the last object in the sentence is the object to which the method is applied In natOOF the objects shall be treated as usual in OOF when they are encountered they are pushed onto the stack The only problem that remains is the treatment of the method within rather than at the end of the sentence Surprisingly this requires only a minor change in OOF s interpret First the normal interpret of OOF will be described Like Forth OOF s interpret reads words separated by blanks in the input stream Then the word is searched for in several lists and is executed or compiled when found depending on the system s state Forth searches vocabular ies OOF searches the lists shown in Figure Two As explained above the methods are searched in the list of methods defined for the class of the object on TOS All methods of the given name are found whose input objects match the objects currently on the stack Of all
31. GIN lt repeat clause gt UNTIL which repeats the repeat clause until the flag becomes true UNTIL terminates the loop when it detects that the top item on the stack is not zero Fib2 uses the implicit ad dition property of LOOP to compute the next Fibonacci number and compare it to the range limit n This method is similar to Wil Baden s method for computing the square root of an integer number Exercise Five The binary series is similar to the Fibonacci series and its members are 1 2 4 8 16 32 64 128 256 512 1024 Write a new instruction BinarySeries todisplay this series of numbers Dr C H Ting is a noted Forth authority who has made many significant contri butions to Forth and the Forth Interest Group His tutorial series will continue in succeeding issues of Forth Dimensions July 1993 August SQRT nl n2 n2 2 lt n1 0 SWAP 0 DO 1 DUP 2 1 LOOP Figure Three Baden s square root routine initial root set nl as the limit refresh root 2n 1 add 2n 1 to sum less than nl loop if else done gt GCD mn gcd BEGIN 2DUP gt IF SWAP THEN OVER WHILE OVER MOD REPEAT SWAP DROP Figure Four Greatest common divisor if mn exhange m and n if m 0 exit loop else replace n by mod m n repeat until m 0 discard m which is 0 Figure Five Fibonacci sequence routines Fi
32. In OOF for each of these repeat global logical variable for system state compileContents of Inword return True if Inword not found keep first unknown as potential verb second unknown found tee notation and can therefore else executeContents of Inword return True if Inword not found endif if if the Verb is empty Verb Inword else OOFErrorCode NotFoundError endif endif until end of Instream or OOFErrorCode lt gt OOFnoError end end of the definition of the method interpret differentiate between meth ods for global objects and cases a special method exists which creates the ap propriate kind of object The methods and push associated keywords onto the stack which automatically cause interpret to find and call the correct This concept follows the tradition of Forth in that it offers small dedicated func tional blockswhich are called in their specific circumstances rather than one big general function with a lot of deci sions and cases Thus special functions and the associated keywords can be added eas ily Another advantage is that it comes for free It makes use of the existing features of OOF no special mechanism such as lots of global flags or local switches need be used It is completely independent of the other significant qual ity of natOOF the variable sentence w o verb sentence with verb within sentence Inwo
33. Instead we provide a one shot word for the DESKJET vocabulary alone This access word is defined on screen 1763 and has some fastForth specific features On line two it grabs the next word name to be found and conditions it at HERE The code on line three searches for it in the DESKJET vocabulary As fastForth has fig Forth style vocabularies this will also search the FORTH vocabulary The syntax on line three is specific to fastForth and will have to be modified for other Forths If the word isn t found the code errors out with ERROR On line four we examine the compile state and compile or execute aS appropriate The word lt COMP gt is specific to fastForth and handles compilation Indirect threaded Forths should use the word Comma instead Sample Application To illustrate how this code can be used a simple application will be shown As my initials are C C I use the figure of a large C with a superscript 2 indicating C squared for my return address on envelopes and elsewhere This monogram is easily coded as seen on screen 1780 If the current output device is the printer or an output file we implement the fancy logo Otherwise on line seven the proof text string C 2 is printed We enter the DESKJET vocabulary to have access to its drivers We set the printer to a pitch of five five characters per inch We then print the upper case C We then go to ten characters per inch We then set up for a six point 6 72nds
34. July 1993 August ou k Z S S Tm 8 SILICON COMPOSERS INC FAST Forth Native Language Embedded Computers Harris RTX 2000m 16 bit Forth Chip 8 or 10 MHz operation and 15 MIPS speed 1 cycle 16 x 16 32 bit multiply 1 cycle 14 prioritized interrupts two 256 word stack memories 8 channel 1 O bus amp 3 timer counters SC FOX PCS Parallel Coprocessor System RTX 2000 industrial PGA CPU 8 amp 10 MHz System speed options 8 or 10 MHz 32 KB to 1 MB O wait state static RAM Full length PC XT AT plug in 6 layer board SC FOX VME SBC Single Board Computer RTX 2000 industrial PGA CPU 8 10 12 MHz Bus Master System Controller or Bus Slave Up to 640 KB 0 wait state static RAM 233mm x 160mm 6U size 6 layer board SC FOX CUB Single Board Computer RTX 2000 PLCC or 2001A PLCC chip System speed options 8 10 or 12 MHz 32 KB to 256 KB O wait state SRAM 100mm x 100mm size 4 layer board C32 32 bit Forth Microprocessor 8 or 10 MHz operation and 15 MIPS speed 1 clock cycle instruction execution Contiguous 16 GB data and 2 GB code space Stack depths limited only by available memory Bus request bus grant lines with on chip tristate SC FOX SBC32 Single Board Computer32 32 bit SC32 industrial grade Forth PGA CPU System speed options 8 or 10 MHz 32 KB to 512 KB 0 wait state static RAM 100mm x 160mm Eurocard size 4 layer board SC FOX PCS
35. L Signed Integer Division Dr Dobb s Journal 83 September 1983 pp 86 88 FORTH and Classic Computer Support For that second view on FORTH appli cations check out The Computer Journal If you run a classic computer pre pc clone and are interested in finding support then look no further than TCJ We have hardware and soft ware projects plus support for Kaypros 100 CP M 6809 s and embedded controllers Eight bit systems have been our mainstay for TEN years and FORTH is spoken here We provide printed listings and projects that can run on any system We also feature Kaypro items from Micro Cornucopia All this for just 24 a year Get a FREE sample issue by calling 800 424 8825 PO Box 535 Lincoln CA 95648 July 1993 August 16 i Mixed length Operators M etc Mm idn dsw DDD M dn d diff DDD Mt inn d prod D M MOD dn mres n quot from f83 com DUP IF DUP R 2DUP XOR R OR 9 DABS R ABS UM MOD SWAP R NEGATE 10 SWAP R IF NEGATE OVER il IF 1 R ROT SWAP THEN THEN 12 R DROP THEN ig 14 15 2 Mixed length Operators M etc 1 23 M dn nquot M MOD NIP 3 MMOD dn ren M MOD DROP 4 5 Ute ud un ut uts unsigned triple DUP ROT UM XR RU SR RD D 6 7 8 UT MOD ut un ur udg 9 R RE UN MOD SWAP ROT 8 Re UM MOD SWAP 18 ROT R UM MOD SWAP R il 8 2SWAP SWAP D R ROT M
36. NCE The original technical conference for professional Forth programmers managers vendors and users Following Thanksgiving November 26 November 28 1993 Asilomar Conference Center Monterey Peninsula overlooking the Pacific Ocean Pacific Grove California U S A Theme Forth Development Environment Papers are invited that address relevant issues in the establishment and use of a Forth development environment Some of the areas and issues that will be looked at consist of networked platform independence machine independence kernel independence Development System Application System Independence Human Machine Interface Source Management and version control help facilities editor development interface source and object libraries source block and ASCII text independence source browsers including editors tree displays and source data base run time browsers including debuggers and decompilers networked development target systems Additionally papers describing successful Forth project case histories are of particular interest Papers about other Forth topics are also welcome Mail abstracts of approximately 100 words by September 1 1993 Completed papers are due November 1 1993 We anticipate a full conference this year V Priority will be given to participants who submit papers ww Earlier papers will be given preference in choosing longer presentation periods John Hall Conference Chairman Robert Reiling Conference Di
37. OOF goes a step further the method that is to be invoked not only depends on the class of the object the message is sent to but depends also on the number and classes of additional parameters This is called multiple polymorphism and will be described in more detail later All these features enforce a structured approach towards programming They support a strategy of stepwise refine ment and relieve the programmer of many burdens such as taking care of special cases Additionally OOF s strong typing makes sure that as many errors as possible are detected at compile time such as sending the message draw to an integer Thus run time errors are kept to an absolute minimum e g hardware errors or buffer overflows natOOF Comes Natural Since natOOF is supposed to be close to a natural language commands are given in the form of a sentence A sentence contains one verb at most and any number of nouns and or prepositions Examples of valid sentences are turn on Motor build Histogram of Image fulle 50 Gramm Pulver in den Beh lter Cursor l schen According to the basic structure of imperative sentences in most European languages a sentence mostly starts with a verb But in natOOF the verb may be placed at any position in the sentence Thus this concept can be transferred to languages other than English which require or enable a different syntax This might appear negligible but in many applications especially non expert users feel
38. UL oO OF FONT ASCII chr select font according to flag SECOND F IF 1 THEN SP WN FE CO DJSIGN ROT 0 lt IF ASCII ELSE ASCII THEN HOLD PRP PEP OpwnHrPow Scr 1751 0 deskjet sequences 1 DJSEQ c cc ct compile seq of ct chars 2 r ae send to deskjet only 3 CREATE COMPILE HERE C 1 ALLOT 4 DOES gt OUT F gt R PRINT IF LI EMIT THEN 5 COUNT TYPE R gt OUT F 6 7 FSEQ Nees cc ct compile seq of ct chars 8 NE send to deskjet only 9 CREATE COMPILE HERE CQ 1 ALLOT 10 DOES gt OUT F gt R PRINT IF LI EMIT THEN FONT EMIT 11 COUNT TYPE R gt OUT F 12 13 DJSEQ TEST1 abc 14 15 debug dummy fastForth on Atari ST Monday 8 3 93 10 12 54 8 58 21 2 93 CRC 17 31 21 2 93 CRC 17 35 c 1985 92 by Charles Curley Forth Dimensions 29 fixed width Courier 10 pitch The Code The start of the code at screen 1749 establishes a num ber of system conditions Line one for example ensures that the fastForth filing facility is present Lines three and four establish the DESKJET vocabu lary Line eight sets the base to decimal saving the existing base for later restoration Line nine loads the code Lines 11 and 12 restore the pre existing fastForth environment The phrase EDITOR FLUSH is use ful during development and was left in once the code was completed to allow changes to be develo
39. ackage for the on line help system and for the graphics package Finally the standard DOS linker can be used to link to any package that creates a DOS standard OBJ file to help support mixed language programming The price is 625 FORTH Inc announced an add on GUI option for its polyForth for 80386 486 systems with VGA The option is an OSF Motif style GUI toolkit It offers low level support in the form of widgets as well as high level support for dialog boxes and menus With the toolkit comes a new version of a full screen Forth editor Source code for the toolkit is included Companies Mentioned FORTH Inc 111 N Sepulveda Boulevard Manhattan Beach California 90266 6847 Fax 213 372 8493 Phone 800 55 FORTH MicroProcessor Engineering Ltd 133 Hill Lane Shirley Southampton SO1 5AF England Telex 474695 FORMAN G Fax 0703 339391 Phone 0703 631441 37 stream of software development It would be a compelling demonstration of Forth s breadth of utility to use it in a service generating role For example Forth could efficiently and effectively generate the file manipulation and file I O services that the POSIX standards deem necessary amounting to forty or more routines POSIX refers to Portable Operating System Inter Continues on page 42 July 1993 August One Screen Virtual Dictionary Gordon Charlton Hayes Middlesex U K I do not feel comfortable with files Forth is a stati
40. agement Where Forth systems don t address a POSIX feature the source code is likely to be targeted to a particular Forth rather than the underlying machine on which the Forth is running By producing precompiled object modules we make use of a more common machine language denominator for code ultimately leading to more code reuse potential POSIX services are ultimately operating system services As such they are expected to reside in memory in a machine language format The programs that are clients of these services need not be affected by the language of origination The process of generating POSIX services from Forth will provide us with an opportunity to learn to write code in terms of a more language independent layered software model Meanwhile this installment of the Product Watch page 37 mentions two fascinating Forth systems One is written in C and therefore could offer the code reuse potential associated with an open development system Another Forth system sports a GUI that imitates X Motif Someone may even want to use it as the basis of development of a display server in accord with the X Window System client server protocol Publicity help offered In the Spring 1993 edition of the MicroProcessor Engi neering catalog we learn of the promotion of Nigel Charig as their Sales and Marketing Manager MPE focuses on its former customers as the primary readers of this catalog so the offer on page two may or may n
41. any other things that it would be inappro priate to include in a standard 1 hope Jack s book is the first of many But I do believe readers will find the current draft better than Houston Shipping Channel water It may not be Perrier but it s at least L A Tap Sincerely yours Elizabeth D Rather Ms Rather is the chairperson of the ANSI Technical Commit July 1993 August tee developing the ANS Forth Ed C Saws Frogs and Princesses Dear Marlin It is with mixed feelings that I renew my membership for yet another year Please let me explain Iam nota programmer butinstead an engineer who must program at least enough to make my hardware designs function I design for two basically quite different realms one is interface cards in a PC type machine that usually includes a user interface and the other is embedded control proces sors usually with no user interface Over the years for the PC and before that for CP M 8080 computers I have written in assembly or Forth With the exception of one sad sorry experience with Forth on a 196 I usually program the particular embedded processor in its assembler A couple of years ago I was dragged kicking and screaming to C because 1 in my work more and more I was am required to be able to look at other people s C code and understand at least a little of it and 2 I have a commitment as a working engineer to be at least minimally competent is such a widely accepted la
42. ate the use of an indefinite loop BEGIN lt repeat clause gt WHILE lt true clause gt REPEAT which repeats the repeat clause and the true clause if the flag tested by WHILE is true When that flag is zero the loop is terminated You may want to test the routine by typing 123 456 GCD Exercise Four The Least Common Multiple LCM of two numbers can be computed by dividing the product of these two numbers by their GCD Write a new instruction LCM which returns the least com mon multiple of two integers The Fibonacci Sequence Fibonacci was the pseud onym of the great mathemati cian Leonardo of Pisa in the Middle Ages He posed a prob lem dealing with the offspring generated by a pair of rabbits seed in fact divide by 65536 Forth Dimensions 25 July 1993 August A man puts one pair of rabbits in a certain place en tirely surrounded by a wall How many pairs of rabbits can be produced from that pair in a year if the nature of these rabbits is such thatevery month each pair bears a new pair which from the second month on becomes productive The sequence will be 1 1 2 3 5 8 13 21 34 55 89 144 233 377 I propose two equivalent solutions in Figure Five To test the routines try Fibl 10000 Fib2 Fibl is a routine using explicit instructions to add the two previous Fibonacci num bers to get the next one It uses the indefinite loop structure BE
43. bject oriented world since they run on their own without being linked to an object The normal executable object is a method A method is invoked when a message is sent to an object e g the message draw is sent to a rectangle object This object knows how to draw itself and calls the appropriate method that paints a rectangle on the screen When on the other hand the message draw is sent to a circle the circle object calls a different method to 17 July 1993 August Figure One Basic principles of natOOF nouns prepositions and at most one verb where e prepositions make the sentences more e verbs specify the action at a position within the sentence where the paint a circle on the screen So we see that each object itself knows best what to make of messages sent to it There is no need for the programmer to provide various ifs or cases for each new class of objects they are all built into the run time system This feature is called polymorphism When a special class of shaded rect angles shall be defined we define ShadedRectangle asa subclass of the class Rectangle and inherit all methods defined for ordinary rectangles e g setCoordinates Only the method draw of course must be redefined such that it paints a shaded rectangle on the screen So a hierarchy of classes is built where each subclass inherits and refines if necessary redefines the properties of its parent As far as polymorphism is concerned
44. bl 1 1 BEGIN OVER U SWAP OVER DUP 50000 U gt UNTIL 2DROP Fib2 n print all Fibonacci numbers less than 50000 display all Fibonacci numbers smaller than n two initial Fib numbers print the smaller number compute next Fib number exit if number too large else repeat discard the numbers 1 initial number SWAP 1 set up range DO DUP U print current number I the next Fibonacci number SWAP prepare the next to come LOOP add current to index if the repeat until sum gt n U print the last Fib 26 Forth Dimensions HARVARD SOFTWORKS NUMBER ONE IN FORTH INNOVATION 513 748 0390 P O Box 69 Springboro OH 45066 You already know HS FORTH gives more speed power flexibility and functionality than any other implementation After all the majority of the past several years of articles in Forth Dimensions has been on features first developed in HS FORTH and many major applications discussed had to be converted to HS FORTH after their original dialects ran out of steam Even public domain versions are adopting HS FORTH like architectures Isn t it time you tapped into the source as well Why wait for second hand versions when the original inspiration is more complete and available sooner Of course what you really want to hear about is our SUMMER SALE Thru August 31 only you can dive into Professional Level for 249 or Produ
45. c language at least with reference to its memory allocation routines and from this it derives much of its simplicity Files on the other hand use disk space in a dynamic fashion They are consequently rather more complex both in the amount of code required to implement them and in the complexity of code in programs that use them Blocks are simple in comparison being merely 1K windows into a larger virtual memory Although this prob ably resides on disk it need not All that is required of BLOCK is that it will accept a number and return a 1K chunk of data that corresponds to that particular number What BLOCK does not provide is any means of organizing this secondary memory system I have seen some attempts to structure block space using dynamic allocation schemes but on the whole they tend to be overly complex and in trying to satisfy every possible need end up not meeting any If we chose a static allocation system however we already have a good model to work from the Forth dictionary It is often forgotten that blocks represent a window into virtual memory The program presented here allows just that and it is simple In fact it is simple enough to fit into one screen although for reasons not entirely unconnected with readabil ity it is presented on three The only thing about BLOCK that will cause us problems is its insistence in slicing memory into monotonously similar 1K portions This we can compensate
46. ce it VERTICAL CREATE W DOES gt W VERT F 2 3 4 DJCR VERT FR DUP gt VERTICAL LNCTR 5 PRINTER LNCTR F LN PG F gt IF PPAGE 6 ELSE CTL M EMIT LMRGN THEN 7 8 9 DECIMAL FORTH DEFINITIONS DESKJET 8 VERTICAL SINGLESPACE 15 ELSE VTAB THEN 20 5 88 CRC 10 28 Scr 1761 0 deskjet margin setup 1 LMARGIN col set left margin in columns 2 ASCII L ASCII a ASCII amp BUILDCMD 3 4 RMARGIN col set right margin in columns 5 ASCII M ASCII a ASCII amp BUILDCMD 6 7 DJSEQ MARGINS 9 disable margin setup 8 print left to right only 29 16 VERTICAL DOUBLESPACE 10 12 VERTICAL 1 5SPACE 20 VERTICAL 2 5SPACE 11 PRINT LNCTR OFF OUTPUT gt PRINTER PNT 12 PPAGE NLIST DESKJET DJCR STOP 13 PRINT EDITOR FLUSH PRINT DESKJET PERF 14 VTAB DESKJET PRINT IF VERT F DUP gt VERTICAL LNCTR The phrase SWAP OVER gives us a Sign flag on the stack below the double precision value for conversion This sign flag will later be consumed by SIGN We then convert our value to an unsigned value ready to be converted Conver sion is started with lt The entire value is converted to a string using S leaving a double precision value of 0 on the stack SIGN does its thing optionally adding a minus sign to the string and eating the signed value left earlier We end conversion with gt which eats the double precision 0 and leave the address and count of the
47. commands or statements between re peat and end will be executed until the CPU goes to sleep If the loop shall be terminated under one condition or shall continue depending on another condition this con struct is extended to repeat sentences until logical expression to terminate sentences July 1993 August while logical expression to continue sentences end In these cases repeat and end are words they can appear without messages being sent to an object The end of the construct is always marked by end Therefore in the following loopings only the repeat statement is men tioned In every loop that will be described until and while statements can be used increasing both the flexibility of the construct and the programmer s control The next case is the loop which shall be executed a specific number of times Hence the repeat clause looks like repeat 3 times If the looping index shall be used within the loop we must define a local integer e g Index and use it as the index repeat with Index 6 times Now Index is the loop count starting at zero and ending at five Calling Index anywhere within the loop will yield the current loop count If the boundaries of the loop shall be defined use repeat with Index from 3 to 8 which will cause Index to run from three to eight The most evolved counted loop repeat statement is repeat with Index from 3 to 8 step 2 introducing the increment of the loop count This
48. ction Level for only 299 Also for each utility purchased you may select one of equal or lesser cost free Naturally these versions include some recent improvements Now you can run lots of copies of HS FORTH from Microsoft Windows in text and or graphics windows with various icons and pif files available for each Talk about THE tool for hacking Windows But face it what I really like is cranking up the font size so I can still see the characters no matter how late it is Now that s useful Of course you can run bigger faster programs under DOS just as before Actually there is no limit to program size in either case since large programs simply grow into additional segments or even out onto disk Good news we ve redone our DOCUMENTATION The big new fonts look really nice and the reorganization along with some much improved explanations makes all that functionality so much easier to find Thanks to excellent documentation all this awesome power is now relatively easy to learn and to use And the Tools amp Toys disk includes a complete mouse interface and very flexible menu support in both text and graphics modes Update to Revision 5 0 including new documentation from all 4 xx revisions is 99 and from older systems 149 The Tools amp Toys update is 15 shipping 5 US 10 Canada 22 foreign HS FORTH runs under MSDOS or PCDOS or from ROM Each level includes all features of lower ones Level upgrades 25 pl
49. d 92 If anyone can provide a rigorous description of the Ratcliffe Obershelp algorithm he would be pleased to hear from them can be maintained or to bomb the program with some fairly useless message such as Division By Zero Error Forth is often used in cir cumstances where the latter op tion is not appropriate The former is best solved by prevention rather than cure Trapping bad data is best done at the earliest possible opportunity before it does any damage rather than letting the inevitable happen and then patch ing up the pieces Certainly there are times when it is not possible to trap dangerous combinations of data until the error and then it is appropriate to use THROW ina low level routine However what I regard as toolbox routines I maintain a li brary of routines I have coded which are applicable to more than one project such as this code are developed without error handlers which I add for particular projects as required Generally this is quite easy and means that the error handlers can be tailored to the application in which they will be Virtual variable ACTIVE V PAGE blk V DP V HERE Virtual IF THEN CREATE DOES gt active V BASE addr active V ALLOT len v dp ACTIVE V PAGE V BASE V DP V HERE V ALLOT 1024 constant B BLK 0 f 8 addr active 4 vaddr v dp r V ALIGN V ALIGNED V g
50. ding to the ancient of the fourth power as well mathematician Euclid If m gt n find GCD n m the numbers The most famous method to find the GCD of VARIABLE XS 10K SIN degree PI 180 SIN COS degree PI 180 COS Figure One Bumgarner s sine and cosine routines 31415 CONSTANT PI 10000 CONSTANT 10K scaling constant square of scaled angle KN nl n2 n3 n3 10000 n1 x x n2 where x is the angle XS SWAP x x n2 NEGATE 10K nl1 x x n2 10000 n1 x x n2 SIN x sine 10K x in radian 10K DUP DUP 10K x x scaled by 10K xs save it in XS 10K 72 KN last term 42 KN 20 KN 6 KN terms 3 2 and 1 10K times x COS x cosine 10K x in radian 10K DUP 10K XS compute and save x x 10K 56 KN 30 KN 12 KN 2 KN serial expansion sine 10K convert to radian compute sine cosine 10K Figure Two Brodie s random number generator VARIABLE RND HERE RND initialize seed RANDOM n a random number within 0 to 65536 RND 31421 RND 31421 6927 RND 31421 6926 mod 65536 DUP RND refresh the seed CHOOSE nl n2 a random number within 0 to nl RANDOM UM nixrandom to a double product SWAP DROP discard lower part Translating the algorithm to Forth we have the code shown in Figure Four This is an excellent example to illus tr
51. dustry because of the ever increasing value of the markets they created To ensure more open access to the royal jewels of the future open specifications for system services are anxiously awaited Forth Dimensions Microsoft wants its applications to be among the first to reach any newly opened markets Open systems will inevitably grab a large share of the operating systems market Plug and play layers of software will delight users through the system extensibility they afford Besides providing the consistency users want API ser vices are labor savers For example graphical applications are no longer directly responsible for drawing window frames or for closing resizing or relocating windows When you consider that half of an application s code supports the human interface a GUI API represents a very large reduction in effort for application programmers Cross platform GUI APIs will soon lead to much more code reuse and labor savings Labor saving concerns may override programmer con cerns over the choice of language Fourth generation data base languages can also lead to labor savings but they tend to be monolithic systems The granularity of software layers APIs has more potential than 4GLs to open up new markets This is because of the broad range of applications areas that layers of software can address A large volume purchaser of computers and software wants to avoid specifying a particular vendors make and model W
52. e Mx dnn d triple intermediate D dd d D dd d UM uu ud U M u u ud same as UM xD nn d UM MOD udu ur uq MU MOD ud u ur udq M MOD dn nr nq Table Three 16 bit n 32 bit d 32768 lt 0 gt 32767 2 147 483 648 lt 0 gt 2 147 483 647 ivi n ivisor quotient remainder 4000 27 148 4 4000 27 149 23 4000 27 149 23 4000 27 148 4 15 July 1993 August divisor are the same and negative if they are not the same The sign of the remainder follows that of the divisor As a result zero applies only to a positive quotient and the remainder cycles through the same values as the dividend passes from a positive to a negative value All this may seem to be nit picking but since Forth is widely used in embedded systems a smooth and consistent transition through the zero point was considered valuable in programming such things are plotters and robot arms So a warming When translating programs from other languages to Forth you should be aware that not all signed integer divisions are the same and that computed data must be compared to expected values References Berkey Robert Positive Divisor Floored Division Forth Dimensions XII 1 May June 1990 p 14 Hendtlass Tim Math Who Needs It Forth Dimensions XIV 6 March April 1993 p 27 part one of a two part series Smith Robert
53. e and transferred by modem in a few hours Although he has bunches of dirt cheap graduate students at his beck and call he says he finds it much less expensive overall to deal with us 4 The suits in the front office might be delighted to hear you ve found a way to save them significant time and money by using a technique that s been used successfully by many of the technology leaders of America No fairy tales needed 5 The system design will probably have been bungled Yes sigh it usually is But even a lot of Forth detractors admit that it s great for developing by successive prototyping the fall back path of choice when the design is fuzzy or non existent Often it s easier to do a prototype of say a user interface than to get somebody to try to imagine on paper how it should look And when the design decisions are being reconsidered Forth s interactivity and flexibility really shine As to the large project issue we ve been involved in numerous 5 20 programmer teams over the years The main difference between these and similar projects using other languages is that each programmer is so productive that you have to be on your toes making sure they re being productive in the right directions Communication and coordination is even more important and there is never enough of it in any project But is this a liability Somehow I ve never heard managers wishing their programmers were slower or les
54. e extended again to include the tools that other programmers have come to expect In the process I hope to include tools that Forth programmers will find useful The FSAT project Gwhich stands for Forth Systems Applications Tools breaks down into several categories Since the ultimate goal of the project is to have a complete UN X like operating system complete with the tools that a UN X user has come to expect along with the tools unique to Forth and some tools that hopefully will emerge at the interface I feel it would be logical to decompose the articles into articles about the tools and articles about the functioning of the operating system and system internals At this point I feel compelled to explain at least part of the title for this article When I first described the concept of Forth Dimensions The FSAT Project or How to Build an Operating Environment Win Friends and Influence People All While Being Politically Incorrect in a Politically Correct Way this series of articles to the editor he said that some would probably feel that the articles wouldn t be politically correct My response to this is twofold the weaselly response is that Im trying to meld a mainstream OS with Forth in such a way that a person comfortable in either would be comfortable with my work The other possibly more accurate re sponse is that if I were worried about being politically correct Id be programming in C In th
55. eceniaiasseclepsibetans eeseanieies 35 Computer Journal 7 16 Forth Interest Group pe centerfold 44 Harvard Softworks 2 0 ecccccccceecscessssssseeeeees 27 Laboratory Microsystems pp 8 Miller Microcomputer Services 00000 23 Silicon COMPOSETS pp 2 July 1993 August 14 Forth Dimensions F83 Arithmetic Walter J Rottenkolber Mariposa California Forth follows the assembler paradigm As a result data is not typed internally and the programmer must keep track of what the data on the stack means In addition operators are not overloaded so different functions must be specified for different data types For example single and double integers require two separate words for addition ie and D In Starting Forth Leo Brodie lists a number of mixed arithmetic operators not part of the Forth 83 Standard that deal with a combination of double and single integer arithmetic Table One Since I occasionally come across source code that uses these functions I thought it would be handy to have them predefined rather than scurry about patching up something at the last moment I use the Laxen amp Perry version of Forth 83 since I still run my ancient Z80 system This Forth includes an eclectic group of mixed and double arithmetic functions both as part of the Forth 83 Standard and as extensions to it Table Two I happily discovered that most of the work had been done already and only simple extensions were r
56. ect them as facts It s a disservice to the Forth community to pass on this stuff without at least checking with some of the folks who have been very successful doing just those things the myths say you can t do So where do think Forth is going During the first decade of FORTH Inc s life everyone was using Fortran and saw no need for a new mainline language Then everyone used Pascal briefly now C But look There on the horizon Its C The fact is that language ike other fashions come and go Mainline languages were designed for a particular purpose and then got popular and started being used for other purposes Forth was designed for a particular purpose to maximize both programmer and code efficiency particu larly in real time applications Lots of people still want to do that Forth hasn t taken over the world not for any technical reason but for a marketing reason no large well known organization has elected to spend a lot of money populariz ing it Until that happens miracle it will continue enabling imaginative companies such as AMTELCO remember Olaf Meding s article a few issues ago to smash their competition and take 80 of the market Would your company like to do that Sincerely yours FORTH Inc 111 N Sepulveda Boulevard Manhattan Beach California 90266 6847 Forth Dimensions Three Piece Logic Dear Mr Ouverson Donald Kenney s article Forth in Search
57. ed by an asterisk The next character is usually a letter indicating a sub July 1993 August category of command This is not always the case as with the character set selection commands The next character is always one or more decimal numeric characters 0 9 indicating a number In some cases such as vertical or horizontal movement commands the value is interpreted literally and may be signed In other cases the numbers are rather arbitrary such as proportional spacing on 1 or off 0 A leading minus sign is permitted This is meaningful in some commands such as horizontal and vertical movement commands Some commands take the numeric value liter ally but a negative value is meaningless such as pitch or points In these cases the result of sending a negative number is unknown and probably silly A leading plus sign is optional where all values are assumed to be positive such as a point size command Where the value may be positive or negative such as a cursor movement command the plus sign is required The numeric value is always followed by a letter If the letter is upper case the command is ended If it is lower case another command in the category follows immediately Printer commands that have the same category and subcategory may be chained The first command is sent with its last character lower case In subsequent commands the escape category and subcategory characters are omitted In the last command
58. ented Forth OOF The nouns can be interpreted as objects that hold data e g Buffer Forth is an untyped language OOF on the other hand is strongly typed Every object belongs to a class type Its class determines what data the object contains and which methods functions are defined that work on the object When an object is called it pushes itself onto the stack E g Valve pushes the object Valve onto the stack The verbs are methods that are applied to objects optionally taking other objects as parameters e g read Methods are not called directly words in Forth are but are searched for at run time in the list of methods available for the object that lies on TOS The prepositions can be interpreted as objects of special classes that help to distinguish between similar sentences by means of OOF s multiple polymorphism These are the fundamentals that support the basic realiza tion of natOOF They make an implementation of verbs prepositions and nouns in OOF straightforward The next step is the switch from the classic postfix notation of Forth to the more natural notation of natOOF which is mostly but not necessarily prefix From Postfix to Anyfix The standard notation in Forth and OOF is postfix i e first push all operands onto the stack and finally apply the operator Expressed in OOF terms the method follows a Forth Dimensions Figure Two The lists that OOF s interpret searches EXECUTE state
59. equired Only M MOD and M required more extensive coding and I thank Tim Hendtlass and the Forth Interest Group for the code in UT and UT All these mixed functions are signed and no run time error checking is done You are obliged to keep both the range Table Three I ve noticed in the programs I use that almost all division is of positive integers As a result I rarely deal with the peculiarities of signed integer division Table Four No nothing is broken Forth 83 uses floored integer division When it was implemented in the early 1980s a great debate ensued between the use of symmetrical and floored division In symmetrical division the more commonly used the quotient is rounded toward zero This leads to a discontinuity in which there are both positive and negative zero quotients and an inversion of the remainder cycling as the dividend passes from a positive to a negative value Both the quotient and the remainder track the sign of the dividend Floored division rounds toward negative infinity The sign of the quotient follows a rule similar to that of multiplication i e positive if the signs of the dividend and Forth Dimensions starting and intermediate values of the signed integers within Mixed Integer Table One M dn d M dn d M dn d M MOD dn nr nq M dn nq MMOD dn nr M MOD dann nr nq triple intermediat
60. ers of the extensive 8051 8052 family Speeds to 30Mhz up to 176 I O lines A D s to 12 bit with 12c interface and Pulse Width Modulators A complete high level AM Research The Embedded Controller Experts 4600 Hidden Oaks Lane Loomis CA 95650 1 800 949 8051 35 July 1993 August A Forum for Exploring Forth Issues and Promoting Forth Fast PORT ware The Impact of Open Systems Mike Elola San Jose California To better understand why open systems are of such key importance to the future of computing you may wish to read UNIX POSIX and Open Systems Addison Wesley Here is how John S Quarterman and Susanne Wilhelm describe the market s motivation to acquire open systems Users want to move programs among machines and employers want to move users among machines Vendors want to sell applications for a variety of platforms and platforms for many applications Everybody wants applica tions that can communicate and systems that can exchange data and information Programmers enjoy the benefits of an open development environment whenever they use debuggers compilers editors and libraries from a variety of vendors in tandem on one project But the path that interoperability has traveled has been a haphazard one I ll examine some of the changes in the course of computing that helped guide the market and software developers towards open systems Some thirty years ago higher level programming lan guages were
61. ery successful kludge used in managing libraries of source code AUTOLOAD FROM n If the next word in the input stream is not found in the dictionary the block number n is loaded from the screen file named in the second next word in the input stream This is an example of another kludge used to manage libraries of source code Both of these kludges suffer from the fact that blocks can be inserted between existing blocks on most block oriented Forth file systems and thus causes references to the wrong blocks Ca val addr Logically AND the character value val with the value at address addr This is another function to build a complete set of operators analogous to c val addr Subtract the character value val from the value at address addr C val addr Add the character value val to the value at address addr A character oriented analog of CELL n A constant value corresponding to the number of address units in a word On most 16 bit Forth systems the value is 2 while on most 32 bit systems the value is 4 CELL n n The constant value CELL is added to the item on the top of the stack Forth Dimensions 11 CELL n n The constant value CELL is subtracted from the item on the top of the stack These two words are primarily used for addressing of adjacent fields CELL nn n The constant value CELL is divided into the value on the top of the stack
62. es During program development they point out the position of bugs in faulty code It is my experience that faulty code is written because of inadequate understanding of the problem In this situation the time spent isolating a bug once detected is time well spent because I come to understand the underlying causes of the problem which is necessary if I am to rewrite the code correctly rather than just patching a duff routine Forth s incremental environment makes detecting bugs easy During program execution error handlers are to trap bad data so that program execution m vs Blocks debate that blocks are notsome sort of poor man s file system but represent a window into a virtual memory They are admittedly underdeveloped as a system but then so are many aspects of Forth This is not a limitation but rather allows the programmer to create tools specifically suited to the task at hand rather than relying on general purpose tools that cannot be ideal for every situation Here we have seen one possible way of developing the block system by mimicking the Forth dictionary allocation scheme I doubt that the constraints of file based system would allow such an extension to be coded so simply and directly Gordon Charlton is the Events and Meetings Secretary of FIG UK and contributes regularly to that chapter s newsletter Forthwrite His last major project was a string pattern matcher which was presented at euroFORML 91 an
63. for and end up with a system which is for me perfectly adequate for most situations Addressing Virtual Memory Rather than dealing with 1K chunks we will treat virtual memory as far as possible as contiguous and addressable within the same range as the host Forth s real memory This means that for a 16 bit Forth we can address 64K of virtual memory and for a 32 bit Forth 4 megs I will refer to the 16 July 1993 August bit case only if your Forth has a different cell width as mine does please change the numbers accordingly If one wishes to use more than 64K we will use 64K pages 64K chunks will cause us fewer problems than 1K chunks In fact we will turn them as far as we can to our advantage by allowing not just 64K chunks but any multiple of 1K up to 64 These we will refer to by name as well as by a unique identifier one cell long to allow them to be manipulated under program control This makes them very much like vocabularies The first word I define is the constant B BLK bytes per block although in fact it remains a magic number even though named as I make much use of the fact that it is a power of two and consequently allows certain bit manipu lations which simplify the math required I make no excuse for this as blocks are infrequently if not never any other length and even when they are they tend to be some power of two bytes in length At any time one page will be addressable and its iden
64. for Novell Since this was the first time had continuous access to a UN X like operating system he had SCO XENIX on a box athome figured I d give it a whirl Imagine my surprise when discovered that it was almost exactly what d ask for in a development environmentif were restricted to C The system is well integrated and it makes a lot of sense for a programmer Now my poor father after having shown his son Forth C and UNIX is writing Microsloth Windows apps in C Well Dad after looking at both Windows and C have to tell you you re safe don t think God Himself could persuade me to take either of them seriously Forth Dimensions Glossary amp val addr Logically AND val with the value at the address addr on the stack The result is stored at addr Pronounced and store Included to make a member of an orthogonal set val addr The value val is subtracted from the value at the address addr Reads and discards the remainder of the input line The same as the dpANS standard word is an immediate word NUMBER addr double true false Attempts to convert the string at addr into a double precision number in the current base if possible and leaves a flag on the stack to signal its success or failure AUTOLOAD n If the next word in the input stream is not found in the dictionary the block number n is loaded This is an example of a not v
65. ften used to write applications but many potential users of application languages do not want to be experts in programming In Germany an object oriented Forth is being used as the base of an application language that allows users to write meaningful programs in their native languages This allows them to concentrate on solutions rather than on the syntax of a computer language 2 4 More on Numbers C H Ting The tutorials continue this time exercising Forth s facility and your familiarity with commonly useful mathematics functions Included sines and cosines random numbers square and cube roots greatest common divisors and the Fibonacci sequence 28 An H P Laserjet Deskjet Driver Charles Curley One of the more popular printers in recent years the Hewlett Packard Deskjet series offers good quality and relatively inexpensive inkjet technology To control its features from within your favorite Forth environment requires only an understanding of the printer s control language and these public domain routines 4 O One Screen Virtual Dictionary Gordon Chariton Files use disk space dynamically and are relatively complex both in the amount of code required to implement them and in the programs that use them But blocks are simple windows into a larger virtual memory requiring only a way of organizing this secondary memory system Attempts to structure block space with dynamic allocation schemes tend to be complex For a static allocation sys
66. he driver It is then up to the driver to embed the value into the appropriate command On screen 1755 we begin to deal with commands of this nature Forth Numeric Output Atthis point a brief digres sion into Forth s numeric out put system is in order Forth stores all numbers internally as binary data Bi nary Coded Decimal BCD is not used Integer values may thus range the full storage capability of the data word or cell in dpANS Forthese on a given implementation The typical Forth system for numeric output converts binary values to text by a process of dividing by the contents of the variable BASE Thus the output string is writ ten into memory a character at a time from right to left Typi cally a double precision value is placed on the stack It may be tested for sign if signed output is desired Conversion is commenced with the word lt begin sharp which initializes the relevant variables One digit may be converted and added to the string with the word sharp The value under conversion may be rendered into text until it is exhausted by the word S sharps Single characters may be added to the string with the word HOLD SIGN consumes the single precision value under the double precision value being converted to insert a minus sign if needed into the string under construction Con version is ended with the word gt Cend sharp which con sumes a double precisi
67. his phenomenon is confined to our present age consider the testimony of that most authoritative of sages Solomon That which hath been is that which shall be and that which hath been done is that which shall be done and there is no new thing under the sun Is there a thing whereof it may be said See this is new it hath been long ago in the ages which were before us There is no remembrance of the former neither shall there be any remembrance of the latter that are to come among those that shall come after Ecclesiastes 1 9 11 Out of Sight Out of Mind The event which set my mind onto this train of thought was the reading of an article announcing the closing of what was described as the foremost engineering library in the world Located in New York city the library suffers from inadequate funding The vast collections of the library are being dissipated throughout the land to other libraries and organizations It is almost certain that such a comprehensive collection will not again be assembled in one location After knowledge is collected and catalogued there remains the matter of preservation I recall several years ago reading of a technique developed by NASA to arrest the deterioration of books printed on acid base paper It seems that even the portion of man s store of knowledge which for the purpose of preservation has been typeset printed and bound is slowly being obliterated as atmospheric moisture Forth Dimen
68. hy discourage competition So the federal govern ment specifies interfaces describing how unbundled soft ware pieces should fit together then asks several vendors to bid on the development of each piece To help establish software components that use the same interfaces and protocols vendors are now proactively seeking open speci fications Interface specifications are the key to open systems Open specifications are clearly needed for network proto cols so that various vendors can produce products that will interoperate They are also important for interfaces to those protocols so application writers can write applications that will be portable to vendors systems Open specifications for interfaces to basic operating system facilities are just as important for portability User interfaces also require open specifications if users are to be able to use more than one vendor s products Open specifications are the key to distributed computing The authors also say that the best open specifications are written by third parties By third parties they mean standard ization committees Under the guidance of ISO ANSI or IEEE rules such committees use a formal and open process to arrive at open specifications An open process allows all interested parties to provide input and allows for updates to standards to track innovations in hardware and software What does this all mean to the average Forth programmer It means that now
69. ied by the basic repeat statement for collections In order to refer to the current display object we must define a local shallow display object here called CurrentDO Before every looping CurrentDO is updated to refer to the next display object in the collection which can thus be manipu lated Figure Four shows how to define the search Figure Five shows an overview of all repeat structures Caveats and Proposed Conventions There are always gremlins hidden somewhere behind a concept In natOOF the major sources of irritation are objects that are forgotten on the stack e g return parameters of methods which are not used They may lead to misinterpre tations of the following code because they can be mistaken as arguments resulting in either a different method being invoked or no method being found at all But since the code for methods tends to be short and concise an inheritance from Forth s well known and proven strategy of factoring it is mostly very easy to find the error Less important is when verbs and nouns or prepositions have the same name Although this is not very likely for semantic reasons verbs do something nouns are some thing the convention below can avoid this error e Nouns start with a capital letter and e verbs and prepositions start with a lower case letter This will also improve readability since these visual clues help to tell objects and methods apart see the code of interpret above as an i
70. ime to time Charles Curley a long time Forth nuclear guru lives in Wyoming Low Cost Next Generation 8051 Microcontrollers With over two decades of Embedded Systems experience AM Research is the only source of single chip development systems which manufactures hardware and writes the development language AM Research provides the tools necessary to get your design to market fast The fully integrated h w and s w systems have standard features such as 8 channel 8 10 or 12 bit A D input All CMOS construction for low power Real Time Clock and EEPROM 2 line by 40 column alphanumeric LCD 16 button hermetically sealed Keypad RS 232 485 serial communications Dual P S cabling connectors 240 page manual and much more Complete and ready to go right out of the box your application can be running in days not months language FORTH allows easy debugging because it runs interactively like Basic but operates 10 or more times faster because it is compiled like C A full screen editor in line assembler communications tools disassembler and decompiler are built in not extra cost options An extensive library of hardware drivers and programming examples are provided with all Developer s Systems or sold separately Other stacking PCB s available Low cost 80C451 and 80C552 systems starting at only 100 Move up to the Engineer s Language for productivity ease of maintenance and comprehensibility Simulate most memb
71. in repeating the repeat clause The difference is that LOOP increments the index by the number on top of the data stack It thus allows the loop index to be incremented or decremented by an arbitrary amount computed at run time LOOP terminates the loop when the incremented index is equal to or greater than the limit Wil uses LOOP in an unconventional way Here the index is used as an accumulator adding the sequence 2n 1 until the sum exceeds n1 At this point n2 left on the stack is the square root of n1 Exercise Two Newton s method to find the square root is a very common method used in programming computers If rl is an approximation to the square root of n then a better approximation is r2 r1l n ri 2 See if you can write a program to find the square root this way Exercise Three The cubes and powers of four of integers can run out of the single integer range very quickly It is therefore not a bad idea to find the cubic roots or power of four roots by raising consecutive integers to the third or fourth power and compare them to the integer whose root you want Write a new instruction CubicRoot to find the Forth Dimensions The Greatest Common Divisor The greatest common divisor GCD of two integer If m 0 GCD m n n numbers is the largest number which can fully divide both Otherwise GCD m n GCD m MOD m n cubic root of any positive integer Try the same for the root two numbers m and n was accor
72. is first priority is the goal to make the system POSIX Portable Operating System Interface compliant Because I am using Forth for a major portion of the development of course it is reasonable to expect that the finished product will be fully as extensible and mutable as Forth itself This flexibility will be a recurring theme throughout the system The user interface is going to be a full implementation of ANS Forth with July 1993 August certain extensions to allow an interface to certain structures that are placed off limits in the standard and other extensions that allow the user to enable certain non standard behaviors Ona more concrete level the Operating System itself will provide standard OS services including multi tasking multi threaded operations demand paging and device indepen dent I O services The Forth model and indirectly the entire OS is based on indirect threaded code with separate address spaces for the dictionary headers data and stacks Although I am writing the OS with portability in mind my first target platform will be the Intel 1386 1486 processor family The operating system will be isolated from user programs by using the protection features of the platform and entry to the system through a single entry point will be enforced On the Intel platform this will be accomplished by making the OS run at a higher privilege level CPL 1 than user tasks CPL 3 The OS procedures themselves will interact
73. is natOOF s form of Forth s do loop which in this case would look like 8 3 do statements 2 loop where the loop count is returned by the predefined word i It goes without saying that the start and end indices as well as the step increment may be any integer global objects results or local objects not just literals times with from to and step are keywords as described above These repeat clauses are defined as meth ods of the class Integer As an example here is the head of the definition of the last described repeat clause Im repeat with Integer Count from Integer Start to Integer End step Integer Increment In addition to the ordinary loop it is possible to link a loop to an object that contains a number of elements One example is an array repeat for every Index into A July 1993 August 22 initializes Index to zero and quits when Index reaches the maximum index into A i e size of A 1 Another example is a collection A collection is basically a list of objects Normally the elements of a collection are not accessed via an index but sequentially one after the other A typical collection contains all objects that are displayed on the screen If you want to find an object by a coordinate e g because you happened to click the mouse at this coordinate a collection of display objects must be traversed i e every display object must be examined This is greatly simplif
74. is series of articles I will attempt to describe the variety of tools that I am using to develop the project For the core Forth system lll be primarily using a macro processing language in tandem with an assembler Once I have the Forth up and running l I be using it to write the device drivers and some of the tools for the Operating System The one system utility that I will be writing with tools other than Forth is the C to Forth compiler When the bits settle the system will include these tools e a C to Forth compiler e several utilities to create and manipulate relocatable object modules and object code libraries e a shameless copy of every FSF Free Software Foundation an admirable group utility I will be using the UN X utilities m4 D yacc 1 and lex 1 extensively in the project Note the numeral one in parentheses refers to the section of the UN X man pages where the description of the programs may be found I will introduce the important features of these utilities in a separate article Remember however that this is a series of articles on a Forth operating system and not a tutorial on UN X utilities so the descriptions will be somewhat brief When I am done I hope to achieve a few goals My number one priority is the merging of the capabilities and strengths of my two favorite environments Forth and UN X From time to time the pursuit of this goal will lead to some bizarre choices on my part Closely paralleling th
75. is the time to use Forth as a labor saving service generating engine that fits into open systems models To meet industry standards it will mean adding conventional library tools to Forth If Forth is proven suitable for implementing many ser vices we can ensure that Forth has a place at the ground level if not also at the application level of future computing and development environments Forth has to become a client of standard system services as well as retain the ability to be a generator of such system services to enter the main Forth Dimensions PProguet Wateln MARCH 1993 J Perham announced the availability of EuroForth 1992 Conference Proceedings 17 50 plus postage and pack ing from MicroProcessor Engineering Ltd MicroProcessor Engineering announced PINC PowerForth a complete Forth system written in C To compile the Forth system from C source use any K amp R or proposed ANS C compiler It is supplied with support for the SunOS CGI and PIXWIN interfaces The cost is 900 MicroProcessor Engineering also announced MPE Modu lar Forth version 3 6 for real time applications on PCs including embedded PCs 80x86 Forth 83 It features a window manager interrupt driven serial drivers file browser and on line help system To break the limit of ten 64K maximum size modules its dynamic linker can be used as an overlay manager Source code is provided for the windows and serial driver packages for the menuing p
76. is was typical of his attitude As soon as was able to discuss one of his areas of expertise intelligently he decided the area wasn timportantafter all and tried to make me look at something else This doesn t just hold in computers he only listens to opera Irish folk and country because like rock classical and jazz Anyway he interrupted a crucial hack of a game file I was trying to give one of my characters in a Dungeons amp Dragons type game extremely high abilities without so much as an Excuse me When asked him if it was possible to get C to do anything more profound than printout lame exclamations he put on a smug smile and handed me a copy of K amp R Brian Kernighan s and Dennis Ritchie s The C Programming Language promptly setit down and went back to hacking OUB save files Eventually primarily because of my father s nagging looked through the book and discovered that there was a class of problems that are trivial or nearly trivial in C that are difficult in Forth Of course the opposite is more usually true worked with either C or Forth for the next several years with a four year intermission for the army using whichever seemed to make the most sense for a given application at the time was also exposed to the UNIX operating system BSD 4 1 during this time and discovered that it had lots of interesting games When got back from the army my father was primarily doing UN X shell programming
77. ited for clarity and length We want to hear from you Smashing Marketplace Myths Dear Mr Ouverson I was appalled by Donald Kenney s article Forth in Search of a Job Forth Dimensions XV 1 I have certainly heard these objections many times and I agree that it s important for all of us to know that these are the fears that haunt some managers What I object to is his bland accep tance of these myths the assumption that these bogeymen are real despite considerable real world evidence to the contrary Let s take them one at a time 1 Integration maintenance bug fixes As we have been serving professional Forth users for 20 years now we and our customers have many examples of both large systems which I ll discuss later and projects that have evolved over many years We have found that Forth wears extraordinarily well In fact our very first customer Bob Barnett of Cedar Rapids Iowa has developed a success ful data entry system over nearly 20 years we first worked with him in the spring of 1974 on at least six different Forth hasn t taken over the world not for any technical reason but for a marketing reason CPUs California Municipal Statistics in San Francisco has a very complex data base program that Chuck Moore first developed in 1976 that is still in use they ve done a lot to it themselves and have called us in a few times to assist with special projects such as porting it to more modern
78. ixed length Operators M etc ME MOD dn nr dg triple intermediate product 2DUP IF DUP R 3DUP XOR XOR R dR ABS R DABS R UT Re ABS UT MOD ROT R NEGATE ROT R 4 IF DNEGATE 2 PICK IF 1 D ROT R SWAP ROT THEN THEN R DROP THEN Me dnn d triple intermediate product JDUP IF 3DUP XOR XOR gt R ABS R ABS ROT DABS ROT UTE AR UT HOD R Oi IF DNEGATE ROT IF i D THEN ELSE ROT DROP THEN THEN Forth Dimensions Towards Markus Dahm Aachen Germany Forth is often used as the basis of an application language e g for instrumentation image processing or device con trol Many users of application languages do not want to be experts in programming but want to concentrate on their application Here Forth offers interactivity extensibility the use of arbitray names and dedicated language constructs At the Lehrstuhl f r Me technik at the Aachen University of Technology we have developed image processing hard ware such as high speed digital filters and transformation processors In an interdisciplinary group of another project we strive to design digital workplaces for radiologists Furthermore student laboratory work for image processing is carried out In some of these applications Forth was or is used However the unusual sometimes quite cryptical syntax of Forth hinders a quick acceptance of the program ming system especially with non experts such as the students radiologists and
79. le response to the action of popping or dotting an empty stack The arrangement reflects the fact that the user in the development environment has free access to the parameter stack Predictable and repeatable responses for erroneous operations reduce con fusion and facilitate diagnostics Note that although opera tions performed with erroneous data obtained from stack underflow may cause a system crash underflow of the parameter stack does not of itself corrupt the system To see the action of the parameter stack buffer cell define a word such as FIZZLE CR 4 0 DO SPACE LOOP Upon entering 1 2 3 FIZZLE the response will be 3 2 1 0 FIZZLE stack empty Forth Dimensions the zero being the content of the buffer cell The entry 1 2 FIZZLE produces on my system the response 2 1 0 8241 FIZZLE stack empty the zero being the content of the buffer cell and the value 8241 being the content of the cell below the buffer cell In embedded applications the need to conserve RAM generally dictates that the buffer cell be omitted However in such an environment the application program typically guards against stack underflow making the cell superfluous Up the Down Staircase Now that you see how all this works allow me to toss in a monkey wrench Technically the terms beneath and bottom are misnomers considering that by convention Stacks grow downward i e toward low memory Thus physically the te
80. llustration Future Work There is a major project coming up where the software will be written in natOOF This will provide experience and insight into this way of programming and into its implemen tation The integrated environment of OOF will be adapted to natOOF natOOF is currently based on the operating system OS9 but will be ported to other hosts such as Apple Macintosh PCs and UNIX workstations Therefore the virtual machine currently written in 68020 assembly language will be redefined in C with modifications to optimize execution speed The portability of natOOF to European languages will be evaluated involving research on the linguistics of natural languages and its significance for natOOF This shall lead to the definition of more complex sentences Perhaps the most ambitious goal is to break down a sentence into individual elements which may be used in any order E g ifa sentence was defined as Forth Dimensions Figure Four Example of a repeat ena structure over a collection Im find Point P in Collection of Display Object Display Object FoundDO shallow Display Object to return to the found Object i Display Object CurrentDO local shallow Display Object to refer to the current DO DOs repeat for every CurrentDO of DOs if P lies in CurrentDO FoundDO gt CurrentDO refer to the found Display Object endif end Figure Five Overview of
81. lue is fixed such as those which set bold or normal weight italic or upright style or which select character sets These could also have been used to define fixed pitch and point sizes buta different route was selected for that see screens 1755 and 1756 On screen 1752 there are defined several character set selectors As I don t use these I see no reason to have them occupy dictionary space and so have them commented out I do however use both Courier and CG Times type faces so these are compiled on screen 1753 Others may be defined ad libitum Below these on lines four through eight are two words to select between the primary and secondary fonts These two words maintain the vari able SECOND which indicates the font currently in use On the next screen several words to control font charac teristics are defined These control super and subscripting bolding proportional or fixed spacing and italicizing Where variables are defined these words maintain the relevant variables Thus far we have dealt only in commands in which the numeric portion is fixed We now look at commands where the numeric field may be influenced by external fac tors An example of this is cursor movement A word pro cessor may deal in multiple July 1993 August columns and may wish to start each column at a precise fixed horizontal position The word processor will have to calculate this value and feed it to t
82. methods found the one with the most input parameters is chosen This ensures that 12 Degrees Valve open invokes another method than Valve open Both methods open are defined as methods of the class of Valve but they execute different pieces of code This is an example of polymorphism and since the difference here lies also in the number of parameters it is also an example for multiple polymorphism In order to allow the operator to appear anywhere within a sentence the treatment of words that were not found or could not be converted to a literal is modified In Forth and OOF in this case an error message is displayed natOOF s interpret on the other hand memorizes the first word that could not be found and proceeds interpreting the input stream In a regular sentence the nouns and prepositions are either parameters or local objects of a method or global objects In either case they are found and are compiled or pushed onto the stack But the verb is neither a parameter a local nora global object and will therefore not be found Its name will be memorized as the potential name of a method When all operands are given the sentence is finished and the verb can be evaluated Enter the global logical variable EndOfSentence When this variable is true interpret tries to interpret the memorized name in the way described above When the verb is the name ofa valid method the method is found and compiled or executed That s all it
83. much more at July 1993 August The basic command of natOOF is a sentence consisting of e NOUNS carry the Data oo cece ccecceeeetseseeeeeees nouns relate to objects readable and select between verbs s prepositions relate to keywords natural language would place it ee verbs relate to methods home when giving commands or writing programs in their mother tongue than in an En glish based computer lan guage These examples illustrate the basic style ideas of pro gramming in natOOF e Use verbs to specify the action at a position within the sentence where the natu ral language would place it e Use prepositions to make the sentences more readable That sounds pretty simple and is easy to understand However this concept is powerful enough to change the style of programming such that programs tend to look like the pseudo code many people write to describe what the program is supposed to do Buthere itis the actual code both readable and executable no translation to a computer language is needed In the examples above commands were given in the form of sentences typical for on line commands in control appli cations They made use of predefined verbs The next sections describe the underlying OOF show how to define verbs and give more details of natOOF s features natOOF is an Evolution of OOF There is a direct correspondence between the syntax elements shown above and the structures of the object ori
84. n C Do I like C Not a whole bunch Almost every line of code is a struggle I find it very powerful I like the user interface I like the hundreds thousands of functions available Last month I bought for less than 50 a commercial supported library that has dozens of functions for user interface windows buttons pull down and pop up windows etc that of course is compatible with my Turbo C What I really miss from Forth is the ability to execute words from the keyboard as an aid to hardware checkout and duly 1993 August debug The edit compile link execute sequence even in the smooth on key turbo environment is clunky compared to the slick quick smooth environment I have with Fifth with its instant compile that occurs when exiting the built in editor remember Fifth it s an F83 variant with a very innovative and elegant coding environment local variables a great word by word trace feature and more Do I still program in Forth Fifth Yes of course There are times when it is perfect A few days ago I needed a quick PC program to check out a quadrature phase rotary encoder for use as a panel mounted operator input device for incrementing decrementing a variable In less than an hour s time I had working code in Fifth So finally to the reason for renewing my Forth Interest Group membership Even though I paid for and registered my copy of Fifth I feel that if I continue to use it I should acknowledge my ap
85. n points 72nd of inch 8 ASCII V ASCII s FONT BUILDCMD 9 10 POINTER CREATE W DOES gt W POINTS 11 12 24 POINTER 24POINT 13 12 POINTER 12POINT 14 6 POINTER 6POINT 15 Scr 1756 0 deskjet character pitch 9 4 88 CRC 10 48 1 PITCH pts set font pitch in chrs inch ASCII H ASCII s FONT BUILDCMD PITCHER CREATE W DOES gt W PITCH 5 PITCHER 5PITCH 10 PITCHER 10PITCH 16 PITCHER 16PITCH 10 20 PITCHER 20PITCH 2 3 4 5 6 DECIMAL 7 8 9 11 12 13 14 15 Scr 1757 0 deskjet underscores 9 4 88 CRC 13 16 1 DJSEQ 1FIXUL amp d1D 2 DJSEQ 2FIXUL amp d2D 3 DJSEQ 1FLOUL amp d3D 4 DJSEQ 2FLOUL amp d4D 5 DJSEQ UL amp d 6 7 1FIXUL VARIABLE UNDER 8 LINER CREATE COMPILE DOES gt F UNDER F wo LINER 1FIXUL 1FIXUL LINER 2FIXUL 2FIXUL LINER 1FLOUL 1FLOUL PR e o 12 LINER 2FLOUL 2FLOUL 13 UL UL UL OFF 14 15 UNDERLINE UL ON UNDER EXECUTE STOP fastForth on Atari ST c 1985 92 by Charles Curley Monday 8 3 93 10 13 00 Forth Dimensions 31 words send commands that control either the primary or the secondary font All other sequences should be defined with DJSEQ which does not send any special characters of its own In either case the string laid down at compile time is then sent to the current output device These two defining words are useful for defining com mands where the numeric va
86. natOOF makes use of these features to enable the programmer to program in a way that closely resembles natural language An appropriate terminology leads to a different view of source code The basic command is a sentence consisting of nouns prepositions and at most one verb where e nouns carry the data e prepositions make the sentences more readable and select between verbs e verbs specify the action at a position within the sentence where the natural language would place it and the sentence ends at the end of the line Since the verb operator may be placed anywhere within the sentence the notations postfix infix or prefix are only special cases of this general concept and can be used and mixed in the personal way of programming in natOOF For our various applications we need a programming system that is usable in rapid prototyping for all kinds of users experts casual users and novices For this purpose the object oriented Forth OOF has been developed Figure One gives a summary of the basic concepts Whats Object Orientation About The fundamental concepts and benefits of object ori ented languages shall be described shortly before diving into natOOF Following the paradigm of object oriented languages in a strict manner everything that exists in OOF is an object There are integer objects or in other words objects of the class integer as well as word objects In fact words are not quite fashionable in the o
87. nguage I chose Turbo C 2 0 because of the really great for a beginner user environment A bonus for me and the thing that really prompted this letter is the very powerful graphical functions BGD One project I am currently working on involves upgrad ing the control system on an industrial machine and part of the upgrade is to replace about a dozen analog panel meters with virtual instruments on a CRT The customer wants a PC type computer for reasons of long term availability of spare parts My natural urge to write the code in Forth was squelched by two things 1 I could not in good conscience leave them with code controlling a very expensive machine with very expensive down time that would be essentially unsupportable they have no internal computer expertise I am not going to be around forever I m an old guy now and finding someone to understand both Forth and their machine is not likely and 2 no Forth I know of has a graphics library of panel meters annunciators bar graphs etc There is no way that in my lifetime I could write in Forth the graphical words to draw these instruments and update them in real time For 250 I bought a complete real time graphics and measurement control library that uses Turbo C s BGD that lets me easily call functions that draw and update needle and arc meters scrolling sweep and x y charts bar graphs annunciators and much more So the real world compels that I write i
88. not on the default search path This word probably also won t work unmodified on a FORTH83 system It is included here only as an example of a kludge that is sometimes used in maintaining libraries of source code in a single block file The following variant is PC FORTH tm specific AUTOLOAD FROM autoload a word from a different file block FIND IF DROP 2DROP ELSE LOAD USING THEN gt scr 12 Basic tools 04 16 93 2 CONSTANT CELL CELL 2 CELL 2 CELLS 2 CELL 2 These words need to be changed for various implementations If you are using a 32 bit FORTH the definitions would be 4 CONSTANT CELL CELL CELL CELL CELL CELLS CELL CELL CELL scr 13 NUMBER 04 23 93 Used to convert a number if possible return a flag stack effect gt address double true false HIDDEN DEFINITIONS s num do miscellaneous setup for number Address 0 0 addr 1 true sign flag 0 ROT DUP 1 CQ ASCII DUP gt R IF 1 THEN 1 1 R gt wt num set up for the while test of number double address dpl flag double address true double address true false false IF DPL NUMBER DUP C BL IF 1 ELSE 1 0 THEN ELSE DROP 0 0 THEN gt scr 14 NUMBER 04 23 93 wl num Code for the while loop double addr double addr dpl flag DUP C ASCII
89. oduced in 18 months and about 30 programmer years software that a prior team had failed to deliver in three calendar years and 100 programmer years Of course we re experts But a few years ago Cameron Lowe of Bell Canada wrote in a magazine article that he and his partner completed in three months a project that their C experts had estimated at three to four years and it was their first Forth project These are not trivial differences Savings of years and tens of thousands or millions of dollars will get most managers attention 3 Cost and availability of Forth programmers As presented the issue is grabbing a body quick for a short time In fact in most communities there exists a group of frus trated Forth programmers who are unhappily programming in C because prospective employers are afraid to use Forth because there aren t any Forth programmers But it is also true that not knowing Forth is a remediable condition We offer courses here almost every month or on site if there are more than three or four people to train There are other trainers as well not to mention books and well documented Forth products that we straightforward to learn Often companies are better served by finding really sharp programmers assembler C etc who are familiar with the application domain in question and letting them learn Forth As much as I hate to say it not all Forth programmers are equally qualified for a particular projec
90. of a Job is alas on the mark At a software conference in February I noted out of about 250 booths the following language vendors zero vendors of Forth Ada COBOL Modula2 one vendor of APL Lisp Prolog Smalltalk two vendors of BASIC Fortran three vendors of Pascal four vendors of C and seven vendors of C In addition most of the libraries and GUI code generators were in C The debuggers were mostly geared toward C and C I heard a great story from a programmer with a major software company He believed C was popular because it behaves like a high level assembler and is available on many platforms His job however was to write tight assembly code for fast math functions and then reverse engineer it into C code that compiles into the original assembly routine The suits thought this made sense Yours truly Walter J Rottenkolber P O Box 1705 Mariposa California 95338 Potable dpANS Forth Dear Mr Ouverson In reading Charles Curley s review of Jack Woehr s new book Forth The New Model I found myself wondering what version of dpANS Forth Mr Curley is using the current version is dpANSS5 by July there will be a new and possibly final draft Over the last year or so many hours have been spent clarifying issues such as those he raises Although he is correct that it is not the place of a standard to serve as a tutorial for complete newcomers to the language leaving the field open for helpful texts such as
91. of the marketplace to which we do have access We can place a couple of ads about our product or service and wait for something or nothing to happen or we can prepare ourselves to go out and meet our prospects face to face We can cringe at objections to Forth and slink back to our offices to lick our wounded egos or we can counter those objections with hard facts and real examples and then demonstrate the validity of our claims proving both our own expertise and Forth s facility by doing a great job and thus creating another happy client Unlike Michaelangelo the Pope is not elevating us to the chapel ceiling if our art is important to us we will erect our own scaffolding one success at a time Sure we d all like to ride the coattails of an endorsement by Bell Labs for example But instead we must rely on business acumen including sales techniques as a necessary complement to our programming skilis We also present in this issue a new author Jim Schneiders FSAT project is of considerable scope tackling the thorny and controversial issues involved in providing a Unix like Forth development environment which will allow among other things compiling C routines into Forth While progressing to that end he promises to provide some interesting utilities to keep us happily occupied while he sweats the details of the big picture And for the sake of those who repeatediy ask Where is the younger generation of Forth programmers
92. on value from the stack presum ably the detritus of conver July 1993 August L Scr 1758 0 deskjet paper sizes vmi 1 DJSEQ 8 5X11 amp 12A 2 DJSEQ 8 5X14 amp 13A 3 DJSEQ A4 amp 126A 4 DJSEQ ENVEL amp 181A 5 DJSEQ DEFAULTPAPER amp 10A 23 2 93 CRC 11 37 6 7 gt VERTICAL n move printhead 48th of in verticaly 8 15 48th gt 720th of in 9 ASCII V ASCII a ASCII amp BUILDCMD 10 11 12 13 14 15 Scr 1759 0 deskjet lpi paper feed draft lq 21 2 93 CRC 17 38 1 DJSEQ 8LPI amp 18D 2 DJSEQ 6LPI amp 16D 3 4 8LPI 8LPI 6 LNFD F 5 6LPI 6LPI 8 LNFD F 6 7 DJSEQ EJECT amp 10H 8 DJSEQ PAPER amp 11H 9 DJSEQ ENVELOPES amp 13H 10 11 FSEQ DRAFTQ s0Q 12 FSEQ LETTERQ s2Q 13 14 15 Scr 1760 0 deskjet topm tlen perf perf 23 4 88 CRC 9 00 1 TOPM Ins set top margin in lines 2 ASCII E ASCII 1 ASCII amp BUILDCMD 3 4 TLEN Ins set text length in lines 5 ASCII F ASCII 1 ASCII amp BUILDCMD 6 7 DJSEQ PERF amp l1L enable perforation skip 8 DJSEQ PERF amp 10L disable perforation skip 9 10 WPSETUP PERF 3 TOPM 63 TLEN 11 12 13 14 15 fastForth on Atari ST Monday 8 3 93 10 13 02 c 1985 92 by Charles Curley i 32 Forth Dimensions 9 DJSEQ L gt R amp k0W 10 DJSEQ BI amp k1w Th 12 13 14 15 swing both ways Scr 1762 0 deskjet output device 1 8 VARIABLE VERT single spa
93. ontrol flow stack manipulators are needed they rarely are Curley seems confused by the fact that the execution behaviors of DO I LEAVE and LOOP have a return stack notation DO CR loop sys I CR loop sys loop sys LEAVE CR loop sys LOOP CR loop sys This relates to the availability of the 7un timeloop control parameters Note the description of the execution behavior of LEAVE Discard the current loop control parameters An ambiguous condition exists if they are unavailable Continue execution immediately following the innermost syntactically enclosing DO LOOP or DO LOOP Now admittedly there are a bunch of syllables in syntactically enclosing So if you still don t know whether that last I will be executed check out the Appendix A 6 1 1760 LEAVE many sections have identically numbered Appendix A sections another good place to keep a tentacle where it says Note that LEAVE immediately exits the loop No words following LEAVE within the loop will be executed Typical use Xm DO IF LEAVE THEN LOOP These appendix notes are explanatory only and do not contain requirements We supplied them where either we or the many people that have contributed helpful comments formal or informal over the years thought extra clarification would be useful There certainly is a place for good books providing tutorials background materials code examples tricks and techniques and m
94. ot apply to you In any case an inquiry wouldn t take much effort Refer to the Product Watch section for MPE s address Here s the context in which the offer was made One of Nigel s comments about Forth has been that many people are not using Forth because they don t know aboul it Consequently we are planning a series of Forth awareness articles for the electronics and computing press If you have an application that your company wants free publicity for contact Nigel so that he can feature it in one these articles Forth Dimensions Om the Back Burner 8 Dead Reckoning Conducted by Russell L Harris Houston Texas The collection cataloging preservation and dissemina tion of knowledge is a matter of concern to all Even the most cursory investigation is sufficient to reveal that the store of man s knowledge is not nearly as secure as one would expect or desire On the whole our knowledge exists as it were in fragments residing in scattered modules of battery backed volatile RAM Occasionally we suffer the irretrievable loss of a portion of man s knowledge At times financial constraint or negli gence allows one of the figurative batteries to expire On other occasions duress sabotage warfare or natural disaster results in destruction or deactivation of a memory module All too often we discover we have no comprehensive backup from which the lost data may be restored Lest you think t
95. part in 10 000 See Figure One This algorithm was first published by John Bumgamner in Forth DimensionsIV 1 To test the routines type 90 SIN 9999 45 SIN 7070 30 SIN 5000 0 SIN 0 90 COS 0 45 COS 7071 0 cos 10000 Random Numbers Random numbers are often used in computer simulations and computer games See Figure Two This random number generator was published in Leo Brodie s Starting Forth To test the routine type 100 CHOOSE 100 CHOOSE 100 CHOOSE and verify that the results are randomly distributed between zero and 99 Exercise One Remember Chinese fortune cookies Write July 1993 August a program which will dispense fortune cookies by selecting a fortune randomly from a fortune database You have to build the database first Square Root There are many ways to take the square root of an integer The routine shown in Figure Three was first discovered by Wil Baden Wil used this routine as a programming challenge while attending a FORML Conference in Taiwan 1984 This algorithm is based on the fact that the square of n 1 is equal to the sum of the square of n plus 2n 1 You start with a 0 on the stack and add to it 1 3 5 7 etc until the sum is greater than the integer whose root you wish to know The number when you stop is the square root The definite loop structure limit index DO lt repeat clause gt inc LOOP is very similar to the DO LOOP sructure
96. ped safely On the next screen we establish five variables SEC OND is used to indicate whether the current font is the primary or secondary font BLD and UL track whether bold or under lining are active The way ULis defined takes advantage of the nature of fastForth in that vari ables are in line in the dictio nary This was done to allow an application to save the state of these two variables with a 2 and restore them later with a2 Hardly transportable but fast This would be useful for a word processor that allowed headers and footers to be de fined so that they could have their own underline and bold characteristics Similarly ITAL is used to track whether italics or upright stroke are in use There is no variable to track fixed versus proportional spac ing but this could be added if necessary LNFD is a holdover from a previous printer driver for the NEC Spinwriter The Spinwriter allows vertical movement in 48ths of an inch making a standard six lines per inch move ment value eight Back when this driver was written for the original Deskjet the vertical movement available was in decipoints 720ths of an inch July 1993 August Rather than re write the word processor the implementor chose to convert from 48ths of an inch to decipoints within the driver see gt VERTICAL infra With the Deskjet 500 a 48th of an inch movement com mand is now available A line feed would move the print head 8 48ths
97. preciation by supporting the Forth community Which is not to say that I like every Forth there are some truly lame products out there I ve kissed a lot of frogs and found few princesses Some of the loudest advertisers have produced the least value But that s a story for another time So okay here s the 40 Sid Knox Helios Systems Oxnard California Total control with LMI FORTH For Programming Professionals an expanding family of compatible high performance compilers for microcomputers For Development Interactive Forth 83 Interpreter Compilers for MS DOS 80386 32 bit protected mode and Microsoft Windows Editor and assembler included Uses standard operating system files 500 page manual written in plain English Support for graphics floating point native code generation For Applications Forth 83 Metacompiler a Unique table driven multi pass Forth compiler Compiles compact ROMable or disk based applications Excellent error handling a Produces headerless code compiles from intermediate states and performs conditional compilation Cross compiles to 8080 Z 80 64180 680X0 family 80X86 family 80X96 97 family 8051 31 family 6303 6809 68HC11 No license fee or royalty for compiled applications a Laboratory Microsystems Incorporated Post Office Box 10430 Marina Del Rey CA 90295 Phone Credit Card Orders to 310 306 7412 Fax 310 301
98. printer with coml Note that in this example there are now two objects called with in the system One is a global object of the class _with and the other is a method But interpret finds the method with only within the definition of input parameters due to the stack effect of the method with When it is found interpret stops searching and thus the global object with is not found because the list of global objects is only searched if no method was found see the search order stated above The global object with is found in all other circumstances Arithmetic and Logical Expressions For non experts especially arithmetic and logical ex pressions are easier to read and write when the normal infix notation is used These expressions are special because everyone has learned a way of writing them whereas few people actually have to handle function calls in everyday life Any deviation from the schoolday notation is likely to cause irritation and errors The arithmetic expression a b in natOOF consists of two integers a and b and the arithmetic operator as usual The operator may be placed anywhere inthe sentence a b a b even a bare valid sentences and may be used according to the programmer s preferences The assignment operator is which is used in the form a cC If a compound expression shall be assigned it must be evaluated as nested sentences as in a b c or a 3 b c d Logical expre
99. ption about your Forth that its address units are bytes and increases it to the next power of two unless it is a power of two itself in which case it does not alter it Do not pass it an argument of zero it does not like it Objects whose lengths have been aligned pack neatly into 1K blocks with no gaps Equally they do not cross block boundaries provided that they start at an appropriate position To illustrate assume I have an array of 200 items each 12 bytes long If I align them I will be dealing with an array of items 16 bytes long four of which will not be used For the cost of this wasted space I gain the advantage of them fitting neatly 64 to a block Of course when I declare the array the virtual dictionary pointer may be at some inconvenient Forth Dimensions position within a block so some of our 16 byte items will end up straddling block boundaries To avoid this we must align the dictionary pointer using V ALIGN This shifts the dictionary pointer if necessary so that it is an exact multiple of the argument passed to it from the block boundary The offset passed to it must be itself aligned This simplifies the code and there is no good reason to pass it anything other than aligned offsets Once we have a data structure established in the virtual dictionary that observes the aligning conventions we can access it very simply using V gt ADDR which converts a virtual address into a real address This it doe
100. r was working on an Atari 800 to divide a 10 000 digit number by a 1 000 digit number and most of the afternoon and the preceding night and noticed hadn t eaten in oh 36 hours or so went into the kitchen and fixed something to eat While en route to my customary eating site I chanced to glance at the previously mentioned tutorial Since was and still am in the habit of reading while eat picked itup and thumbed throughit was struck by the fact that it looked like it would be a lot easier to solve my problem in Forth than in BASIC spent the next two weeks figuring out enough about Forth to do it after which was hooked During this time my father was rapidly acquiring a sizable library of Forth tutorials manuals and essays He was working in Atari s Coin Op division which was very interested in Forth at the time Over the next couple of years read and reread every thing he had on Forth During that couple of years he was laid off from Atari went to work for a small company named Buscom which went under and went to work for Zilog Near the end of the couple of years was recompiling my Forth kernel about once a week and using it to hack save files for a game My father who had shown so much interestin my mastery of Forth up to that point came to me one day and said Well nobody uses Forth anymore Everyone s programming in C now Here let me show you how to get C to print out Hello World Th
101. ramming language In that overrated and specious environment the combination of ill chosen symbology and convoluted rules makes the application and manipulation of pointers a matter of Byzantine complexity fraught with peril for tyro and adept alike The Ups and Downs of Stacks The stack pointer S holds the address of the top of the parameter stack i e the address at which the most recent stack entry resides The application programmer typically has no need to access the stack pointer should however the occasion arise the word S has been defined to push the pointer onto the stack User variable S0 holds the address of the cell immediately beneath the base of the stack Conveniently the same address marks the start of the terminal input buffer sometimes called the input message buffer When execution of a word such as QUIT calls for the parameter stack to be cleared the address in S0 is copied into the stack pointer whereupon the value zerois pushed onto the stack Thus in the condition that the stack is empty the stack pointer addresses the cell immedi ately above the cell addressed by S0 An attempt to dot the empty stack produces the display 0 stack empty Words such as DEPTH which access the stack pointer take into account the fact that the empty stack actually has one entry namely the buffer cell containing the value zero Presence of a buffer cell containing a known value ensures a predictable and repeatab
102. rchitectures are making it easier for new layers of software to be introduced Libraries have long provided a tool for isolating software into layers Now dynamic linking adds yet another tool for layering software recently dropped a system extension into my Macintosh s system folder which expanded my system s services to include support for DOS file systems on 3 5 disks This was achieved so easily due to the Mac s layering of software Without changing any of my applications I can now issue commands from them to read or write a DOS formatted floppy In our present situation it is hardly likely that a trend towards downsized operating systems will develop Today the construction of applications takes place upon a substrate of operating system services GUI services and a number of other specialized API services A key to the success of system software involves satisfying the desire of computer users for consistent services Users don t want to learn six different ways to establish a network connection or three different ways to print within three different applications These APIs have continuously eroded the role of the programming language down to a lesser role that of enabling communications and coordination of the more important services provided outside the language itself Microsoft has become one of the most profitable and most admired companies within the U S economy DOS and Windows are the royal jewels of this in
103. rd is unknown be used in normal postfix oriented OOF too New keywords can be defined at any time just by defining a new class and an more readable Or they can differentiate methods of the same name but different meanings as in lay windowl onto window2 as opposed to lay windowl under window2 Because onto and under belong to different classes interpret is able to differentiate between the two methods called lay In the first sentence objects of the classes window_ontoand windowlie on the stack when a method of the name lay shall be found If a method lay for objects of the class window with exactly these input parameters exists it is found and executed or compiled depending on the system s state In the second sentence the presence of objects of the classes window under and window on the stack cause a different Lay to be found Incidentally in the same manner OOF is able e g to July 1993 August object of this new class In order to make this process even easier a class keyword is predefined The definition keyword with creates both a new dass _with and the object with of this new class plus a method with which is used within the definition of input parameters of a method As an example the method connect shall be defined that connects a device with a port Im connect device source with port target It can then be used e g in the sentence Forth Dimensions connect
104. rector Information may be obtained by phone or fax from the Forth Interest Group P O Box 2154 Oakland CA 94621 510 893 6784 fax 510 535 1295 This conference is sponsored by FORML an activity of the Forth Interest Group Inc FIG The Asilomar Conference Center combinesexcellentmeeting and comfortable living accommodations with secluded forests on a Pacific Ocean beach Registration includes use of conference facilities deluxe rooms all meals and nightly wine and cheese parties
105. repeat end structures repeat while until end The body of every repeat end structure can contain any number of while and until statements The following shows only the repeat clauses repeat N times repeat with Index N times repeat with Index from Start to End step Inc repeat for every Index into Array repeat for every Element of Collection THIRTY DAY FREE OFFER Free MMSFORTH GAMES DISK worth 39 95 with purchase of MMSFORTH System CRYPTOQUOTE HELPER OTHELLO BREAK FORTH and others Forth Dimensions 23 copy N bytes from Source to Destination it shall be possible to call it by typing from Source copy N bytes to Destination without redefining the sen tence This will hopefully lead to fewer necessary references to manuals and to fewer errors It will be no mean feat to achive this without resorting to megabytes of artificial intelli gence Stay tuned We hope our work will not be misused for military purposes We will not take part in any military project References OOF an Object Oriented Forth M Dahm euroFORML 91 Proceedings Forth Interest Group Object Oriented Forth M Dahm Forth Dimensions May June 92 XIV 1 Forth Inter est Group One Screen Unified Control Structures G Charleton Forth Dimensions Jan Feb 1993 CXIV 6 Forth Interest Group Markus Dahm earned his Dipl Ing elec trical engineering in 1987 at
106. ring manager file blocks sector mapped blocks x86 amp 7 assemblers PRODUCTION LEVEL 499 Metacompiler DOS ROM direct indirect threaded systems start at 200 bytes Forth cores from 2 kbytes C data structures amp struct compiler MetaGraphics TurboWindow C library 200 graphic window functions PostScript style line attributes amp fonts viewports ONLINE GLOSSARY 45 PROFESSIONAL and PRODUCTION LEVEL EXTENSIONS FOOPS with multiple inheritance 79 TOOLS amp TOYS DISK 79 286FORTH or 386FORTH 299 16 Megabyte physical address space or gigabyte virtual for programs and data DOS amp BIOS fully and freely available 32 bit address operand range with 386 ROMULUS HS FORTH from ROM 99 Shipping system US 9 Canada 21 foreign 49 We accept MC VISA amp AmEx An H P Laserjet Deskjet Driver Charles Curley Gillette Wyoming A driver for Hewlett Packard PCL Level III in Forth is shown Forth s CREATE DOES gt facility and numeric text output are illustrated Historical Note The version of Forth used here is fastForth a 68000 JSR BSR threaded Forth described in Curley Optimization Con siderations Forth Dimensions XIV 5 The code specific to fastForth is related to I O vectoring vocabulary manipulation and compilation which will be illustrated below Implementation on other Forths should be fairly easy Being figForth in style variables are initialized at compile time by a
107. rm a future application ROM address into the corresponding address in the virtual application dictionary residing on the development system Finally for diagnostic purposes we require a word to compute the inverse transformation i e a word to deduce the application ROM address from the virtual dictionary address In a later column we will choose appropriate names for each of the pointers and for each member within the set of support words In Retrospect a Preview of Coming Attractions et cetera A number of these columns may appear to be simply a review of material which has been presented in books such as Starting Forth However what I am trying to do is illuminate obscure aspects of Forth for which I have found the available documentation to be either incomplete or non existent These aspects must be thoroughly understood if one is to attempt his own Forth implementation Moreover it is not sufficient merely to know whatanother implementor has done you must understand why he did it in the manner in which he did it Your environment may call for a different technique or you may be able to devise a superior scheme Meanwhile has anyone attempted to take the assembler presented in column 4 from working prototype to final form Has anyone built the trainer presented in column 5 Are there any intelligent and attractive single women who would like to date a Forth Dimensions author Does anyone out there understand the abbreviation R
108. rminal input buffer is at a bigher address than the buffer cell at the base of the parameter stack The rationale for implementing a stack such that it grows downward is the ease with which the address of a stack item may be developed one need only adda positive integer to the stack pointer At this point you should pencil a diagram in the margin or turn to the diagrams in Starting Forth to ensure you understand the arrangement Incidentally if you don t al ready have a copy of Starting Forth by all means obtain one ASAP a beiter investment you seldom will make Inasmuch as underflow of the return stack is not a contingency for which one makes provision other than a reset button which should be a part of every system no buffer cell is provided for the return stack Thus the first user variable resides immediately below the first cell of the return stack and the return stack pointer R is initialized to the value residing in the user pointer U Again note that since the return stack grows downward the physical address of the first user variable is bigherthan the address of the base of the return stack The reason no provision is made for underflow of the return stack is akin to the reason airlines provide no parachutes for the passengers underflow of the return stack is a catastrophic event the result of a fatal programming error creating a system condition from which recovery is all but impossible A copy of the top item of the
109. ro tripping loops with a decrementing index do not work correctly Consider the following definition EXAMPLE n 0 DO just once 1 LOOP Those who doubt my assertion may wish to work out what argument should be passed to EXAMPLE to cause it to print the string just once just once v is used to move data from real to virtual memory V fetches data from virtual to real memory It takes as argu ments a virtual source address a real destination address and a length It returns the address of the buffer to which the data was moved Sometimes the most difficult part of coding a word is deciding on its stack effect This was the case with v which accepts arguments like MOVE but returns an address which points to the requested data sort of like This means it does not consume its arguments as is generally accepted to be good style but in practice this turns out to be a useful arrangement Using Virtual Memory Although we have done what we can to make disk memory look like RAM it should be borne in mind that this is not RAM and behaves differently in some respects In particular access times can vary Given say a two dimen sional array of integers that is stored on disk in row major format attempting to index through the array downa column will be a lot slower than traversing along a row as all the elements in a given row are likely to be on the same block whereas elements in a given column will be spread over
110. s by turning the virtual address into a block number and offset It adds the block number to the active base block loads that block and adds the offset to the address returned by BLOCK It is worth remembering that addresses within blocks are of the moment only and should be used immediately or the datum copied to some safer buffer You also need to UPDATE when modifying data For what it s worth I believe blocks should be updated automatically unless specifically inhibited That way instead of being in real danger of losing new data by forgetting to update you run the less likely risk of losing old data in the event that having modified a block you decide against keeping the changes and forget to inhibit updating And finally as my mother used to say don t forget to FLUSH when you have finished Addressing Larger Structures Not every data item will be conveniently less than 1024 bytes long Equally you may not be able to afford the wasted space that aligning implies and it can get pretty horrendous when say an item is 513 bytes long and you lose almost half of every block This can be overcome at the cost of loss of speed this is one of those classic speed memory dilemmas that occur almost everywhere in computing ve and V can be used to access data items that do not observe the block disciplines and are a little more complex They are however very similar With the exception ofa little stack manipulation at the start
111. s productive Also since you can do a particular job quicker and with a smaller team in Forth some team management issues July 1993 August Elizabeth D Rather President solve themselves Readability is an issue in every language as are other subjective style issues We have had great success by establishing in house coding standards that everyone follows As a result you can t look at any of our code and guess who wrote it and programmers never feel the discomfort of having to cope with someone else s idio syncratic style Other successful large shops do the same It matters less what those styles are than that they existand are observed Shared data and other technical issues are handled pretty much the same in Forth as in other languages The details are all different but the principles are the same 6 The controls won t adapt My experience is that proce dures simplify We have developed some tools for configuration management as have other shops that we are reasonably comfortable with although there s always room for improvement Federal Express is pretty formal and report their procedures adapted to Forth well Sun Microsystems which uses Forth in the Open Boot on every SPARC Station uses the UNIX tools The basic problem here is that Mr Kenney is swallowing these common myths whole unexamined and untested They make great rationalizations but there s too much contradictory evidence to resp
112. sions activates the acid residue from the paper making process An Obiter Dictum Regarding the Obfuscation of Abbreviation In every phase of its existence from initial recording to ultimate retrieval knowledge is subject to corruption One mechanism by which knowledge is obscured and obliterated is the insidious and damnable practice of abbreviation As an example consider the term dead reckoning Even Webster apparently is unaware that the term is actually an abbrevia tion the lexicon only indirectly sheds light on the etymology defining dead reckoningas determination without the aid of celestial observations of the position of a ship or aircraft deduced from the record of courses sailed or flown the distance made and the known or estimated drift The fact is that the word dead in the term dead reckoning is simply a mispronunciation of the abbreviation ded Thus indolence and carelessness expressed through abbreviation and mis pronunciation respectively have given birth to the nonsen sical term dead reckoning Having survived this brief lamentation and etymological digression the astute reader will recall that we are in the process of examining metacompilation an activity which as you by now may have deduced calls for a considerable amount of dead reckoning Whereas navigators reckon in terms of geographical coordinates programmers reckon in terms of addresses within the address space of a computer Navigators deal
113. ssions and comparisons are evaluated and assigned similarly However in applications where many calculations must be made this is still too cumbersome An entirely different concept would implement as a parser that interprets the sentence separately This parser could also implement operator precedence such as and before and This approach turns away from Forth s idea of single smart tools rather than one complex function but on the other hand promises to provide the easiest i e the usual syntax for compound expressions Special Words the is it s and the Parentheses Some special words make programming easier and improve readability They will now be introduced The article the can be added anywhere in a sentence It is a word with no function but to make the sentence look more natural e The auxiliary verb is was defined for the same reason it may be used anywhere within a sentence to make it more Forth Dimensions readable The parentheses and are used to nest sentences e g read into next Buffer from Instream or as shown above in the examples for nested arithmetic expressions Here the object that follows Buf fer in a list is fetched first then this buffer is filled from the Inst ream The implementation is simple is a slightly modified inter pret that is terminated by the immediate word e The pronoun it may be used to refer to the object that was on TOS at the beginning of
114. string on the stack We now recover the field size from the return stack subtract the length of the string from it and print the appropriate number of spaces Finally we TYPE the string out 7 88 CRC 17 50 Numeric Commands With that understood we are prepared to build the code needed toembed numbers into commands This is done with the word BUILDCMD on screen 1755 This word takes as its arguments three ASCII charac ters anda single precision num TYPE 2DROP sion and leaves an address and count ready for TYPE or other text output words The location where the string is built is system specific not re entrant The system may guarantee the buffer to be valid only between lt and gt or shortly thereafter This possibility encourages the programmer to use the string as quickly as possible Conversion to any reasonable number base and some unreasonable ones may be done by changing the contents of the variable BASE This may be done during or before text conversion To illustrate how this all works we will examine the fastForth word D R identical to the fig Forth version It is used to place the signed output of a double precision value right justified in a field of given size type signed d in field of size fld gt R SWAP OVER DABS lt S SIGN gt R gt OVER SPACES TYPE gt R places the field size onto the return stack for later use Forth Dimensions ber These will be built into a
115. t If you re doing a time critical embedded system training a C program mer familiar with the processor and application in Forth will probably produce a better result than using some July 1993 August body whose experience is limited to PCs and high level Forth In fact a good C or assembler programmer trained in Forth and using Forth will very likely do better than the same person using C Re read the item about Cameron Lowe above we hear many such stories When I talk with folks running the larger Forth shops I occasionally ask whether programmer recruitment has been a problem Although they would all rather have more top notch Forth programmers besieging them with resumes they generally have no serious complaints As to cost the important thing to remember is the overall cost of getting the project done not the hourly fee for the programmer What you want is the best qualified person who will do the best job for the best overall price We have long happy relationships with people all over the country who have found it cost effective to deal with us for things ranging from small tweaks to an existing system to major projects For a number of years for example we ve supported Bob Gherz an astronomer at the University of Minnesota who has a polyFORTH based telescope con trol program that he runs at three different observatories He can call us on the phone ask for some little thing and we ll likely have it don
116. t ADDR V ALIGN len b blk min 1 v here 2dup and or 1 v dp ELSE 2drop V ALIGNED len len 0 swap 2 1 DO drop i dup LOOP V gt ADDR vaddr addr 0 b blk um mod v base block d Virtual V YVe weed variable FIX update fix FIX fix execute Finally I prefer to program without a net so to speak I write V addr vaddr len code just as responsibly without a gt r BEGIN x nagging compiler such as those WHILE b blk 2dup 1 and r min that other languages appear to insist on as with one Perhaps even more so as I know it is down to me to get it right rather than relying on a crutch VR 3 Y swap fix It is often forgotten in the Files gt r 2dup v gt addr fix r move r swap r swap r gt r gt swap gt r REPEAT r gt drop 2drop vaddr addr len addr gt r dup rot r gt v update fix July 1993 August 40 Forth Dimensions Back Burner continued from page 43 interpreter is sometimes called the immer interpreter in contrast to the extinterpreter which is sometimes called the outer interpreter The code field of a Forth word is a pointer The parameter field of a word defined with contains at least one pointer and may consist of nothing more than a string of pointers Although pointers are basic to programming I never cease to be amazed likewise amused by the treatment of pointers in the C prog
117. t Group Inc respectively Any reproduction or use of this periodical as it is com piled or the articles except repro ductions for non commercial pur poses without the written permis sion of Forth Interest Group Inc is a violation of the Copyright Laws Any code bearing a copyright no tice however can be used only with permission of the copyright holder The Forth Interest Group The Forth Interest Group is the association of programmers man agers and engineers who create practical Forth based solutions to real world needs Many research hardware and software designs that will advance the general state of the art FIG provides a climate of intellectual exchange and benefits intended to assist each of its mem bers Publications conferences seminars telecommunications and area chapter meetings are among its activities Forth Dimensions ISSN 0884 0822 is published bimonthly for 40 46 52 per year by the Forth Interest Group c o TPI 1293 Old Mt View Alviso Rd Sunnyvale CA 94089 Second class postage paid at San Jose CA POSTMAS TER Send address changes to Forth Dimensions P O Box 2154 Oak land CA 94621 Forth Dimensions LELIGrS Letters to the Editor and to your fellow readers are always welcome Respond to articles describe your latest projects ask for input advise the Forth community or simply share a recent insight Code is also welcome but is optional Letters may be ed
118. tem however we already have a good model to work from the Forth dictionary GI Departments 4 Editorial Call for contest entries myth breaking C ing Forth 5 Letters Smashing marketplace myths three piece logic potable dpANS Forth C saws frogs and princesses 14 Advertisers Index 36 Fast Forthward The impact of open systems 43 On the Back Burner Dead reckoning Forth Dimensions 3 July 1993 August Ssclitorial What is the ideal Forth development environment Opinions range from bare bones fig Forth simple maybe elegant to F PC rich to hardware implementations fast graphical interfaces contemporary object oriented post modern etc Of course how you define a development environment will depend on whether you are looking at the issue from within the Forth community the larger software community or the world of embedded systems Whatever your perspective you still have time to share your expertise and opinions and win up to 500 The deadline for entries in the Forth Dimensions Forth Development Environments contest is August 1 1993 Completed papers hard copy and diskette please must be received at our office by that date The theme is the same as for the upcoming FORML conference and papers for that event are also eligible for the FD contest ifthey are received by the contest deadline just mail a separate copy to
119. the Univer sity of Technology Aachen Germany and his M Sc computing science in 1988 at Imperial College London U K He has been a research assistant since 1989 at Lehrstuhl f r Messtechnik in Aachen working on user interfaces for medical image workstations and natural language programming for non experts July 1993 August FortH TuToRIAL LESSON 5 More on Numbers C H Ting San Mateo California Sines and Cosines Sines and cosines of angles are among the most often encountered transcendental functions useful in drawing circles and many other different applications They are usually computed using floating point numbers for accuracy and dynamic range However for graphics applications in digital systems single integers in the range from 32768 to 32767 are sufficient for most purposes We shall study using single integers the computation of sines and cosines The value of the sine or cosine of an angle lies between 1 0 and 1 0 We choose to use the integer 10000 in decimal to represent 1 0 in the computation so that the sines and cosines can be represented with enough precision for most applications Pi is therefore 31416 and a 90 degree angle is represented by 15708 Angles are first reduced into the range from 90 to 90 degrees and then converted to radians in the ranges from 15708 to 15708 From the radians we compute the values of sine and cosine The sines and cosines thus computed are accurate to one
120. the left margin Paging and moving to the left margin are handled in a raw printer driver in the PRINTER vocabulary and are notshown here We then establish the defining word VERTICAL and use July 1993 August 34 that to make several spacing options available in the FORTH vocabulary Almost the last thing to do is to establish a method of hooking the driver into fastForth s I O system In fastForth the words EMIT TYPE GOTOXY PAGE LIST and CRare all vectored through the user area The word OUTPUT gt allows the programmer to construct a list of words to fill those vectors This is done in the word PRINT on line 11 The run time code associated with OUTPUT gt stuffs the execution vectors and then returns execution to the calling word This means that if we want to condition the printer after setting the vectors we must do that in a calling word This is done in PRINT on line 13 Other printing conditioning could be added after the call to PERF Finally on this screen we define a word for vertical tabbing When the printer is the active output device we simply command vertical movement otherwise we use the native vertical tabbing word It would be convenient to be able to reach into the DESKJET vocabulary from time to time without playing Forth Dimensions games with vocabularies One could implement Brad Rodriguez s word FROM which reaches into a given vocabu lary for a one time access e g FROM EDITOR TEXT
121. thought to hold great potential as the founda Now is the time to use Forth as a labor saving service generating engine that fits into open systems models tion upon which applications could take form Algol BASIC and Fortran were among the programming languages thought to be able to displace non portable assembly language programming The application programmer would be trained to use a high level programming language That training and an acquired understanding of an application domain should lead to a successful application About twenty years ago timesharing multi user operating systems became commonplace for mainframes and mini computers These operating systems absorbed many of the services once provided by early programming languages job control languages and computer operators As integrated circuits became more dense RAM memory devices and microprocessors reshaped the industry As part July 1993 August of a memory resident kernel of services an application service routine could rapidly gain control of the computer As processor performance and memory increased the overhead of a co resident operating system eventually became a moot objection Presently single user PC operating systems are heavily laden with services too often making PCs very memory hungry Graphical user interfaces are fueling this growth as well as other services with end user appeal such as network ing Evolving tools and software a
122. through a monitor that has a single entry point and has a higher privilege level than the OS procedures CPL 0 In short I envision a single user multi tasking operating system with the flavor of UN X and the power of Forth and UN X I hope to enable programmers familiar with either Forth or C to be immediately productive My hope is that when the C programmer stops writing code long enough to realize what a pain in the butt it is to write C he or she will be pleasantly surprised to find that they are in an environment where they can be immediately comfortable being more productive using Forth of course lI can t see any way a C programmer can gain the benefits of Forth without using Forth At this point I think I should mention some caveats This system will be a development system conforming to my sometimes quirky needs As such trying to write the Great American Payroll Cruncher on it will probably be a waste of resources The system will support some security buta truly dedicated hacker with a single password on the system can probably find a way to get into everything on the system Because the system uses cooperative multi tasking use as a timesharing multi user operating system is not advised As a large part of these articles will discuss the tools I developed to enable me to do this project I figure it s only fair to start with a few tools The source code accompanying this article is a short selection of the Forth
123. tifier available in the variable ACTIVE A page is declared using V PAGE V PAGE takes a block number as an argument This is the base block for the page At instantiation the dictionary pointer for that particular page of virtual memory is set to zero A page is made active by mentioning its name or by storing its identifier into the variable ACTIVE The base block for the currently active page is available at the address returned by V BASE This in practice turns out not to be terribly useful It could be used in calculating the last block a page occupies but I usually have a fair idea how large my data structures are anyway so have not implemented that function It would be quite simple if required V BASE is included because I habitually try to name fields in composite data structures rather than deal directly with offsets More usefully V DP gives us access to the dictionary pointer for the active page although generally this should be addressed by V HERE and V ALLOT These are analogous to HERE and ALLOT hence the names Aligning Within Blocks Addressing a datum that lies completely within one block is easier than addressing one that straddles one or more block boundaries This probably goes without saying Therefore whatever we can do to encourage entries into the virtual dictionary to fit neatly within blocks should be done V ALIGN and V ALIGNED are used for this V ALIGNED takes an offset in bytes again I make an assum
124. us price difference between levels Source code is in ordinary ASCII text files HS FORTH supports megabyte and larger programs amp data and runs as fast as 64k limited Forths even without automatic optimization which accelerates to near assembler language speed Optimizer assembler and tools can load transiently Resize segments redefine words eliminate headers without recompiling Compile 79 and 83 Standard plus F83 programs PERSONAL LEVEL 299 NEW Fast direct to video memory text amp scaled clipped windowed graphics in bit blit windows mono cga ega vga all ellipsoids splines bezier curves arcs turtles lightning fast pattern drawing even with irregular boundaries powerful parsing formatting file and device I O DOS shells interrupt handlers call high level Forth from interrupts single step trace decompiler music compile 40 000 lines per minute stacks file search paths format to strings software floating point trig transcen dental 18 digit integer amp scaled integer math vars A B IS C compiles to 4 words 1 4 dimension var arrays automatic optimizer delivers machine code speed PROFESSIONAL LEVEL 399 hardware floating point data structures for all data types from simple thru complex 4D var arrays operations complete thru complex hyperbolics turnkey seal interactive dynamic linker for foreign subroutine libraries round robin amp interrupt driven multitaskers dynamic st
125. y and Suggested Reading Be advised most of the works will cite are either documentation for products or out of print or documentation for products thatare no longer available If the work is the documentation for some thing you may be able to obtain it from the vendor They will probably sell the documentation for a substantially smaller sum than the actual product The books that are out of print or the documentation for unavailable products will be harder to come by In most cases the documentation for the later products will suffice If this is not the case I will be sure to point it out The out of print books will probably be found in secondhand bookstores or by asking small volume publishers to reprint a very few copies PC FORTH v1 26 Reference and User Manual The documentation provided with Laboratory MicroSystems Inc s PC FORTH version 1 release 26 this is no longer available Contact LMI at P O Box 10430 Marina del Rey California 90295 Jig Forth Cross Compiler The documentation for version 1 0 of the Nautilus Systems cross compiler Dr Dobb s Toolbook of Forth vols 1 amp 2 A fairly wide ranging treatment of various topics related to Forth Volume 1 was edited by Marlin Ouverson and deals with more nuts and bolts Volume 2 was edited by the editors of Dr Dobb s Journal Forth Encyclopedia A detailed description of each fig Forth word with source code for all high level words By Mitch Derick

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