2 \ A sometimes minimal FORTH compiler and tutorial for Linux / i386 systems. -*- asm -*-
3 \ By Richard W.M. Jones <rich@annexia.org> http://annexia.org/forth
4 \ This is PUBLIC DOMAIN (see public domain release statement below).
5 \ $Id: jonesforth.f,v 1.13 2007-10-07 11:07:15 rich Exp $
7 \ The first part of this tutorial is in jonesforth.S. Get if from http://annexia.org/forth
9 \ PUBLIC DOMAIN ----------------------------------------------------------------------
11 \ I, the copyright holder of this work, hereby release it into the public domain. This applies worldwide.
13 \ In case this is not legally possible, I grant any entity the right to use this work for any purpose,
14 \ without any conditions, unless such conditions are required by law.
16 \ SETTING UP ----------------------------------------------------------------------
18 \ Let's get a few housekeeping things out of the way. Firstly because I need to draw lots of
19 \ ASCII-art diagrams to explain concepts, the best way to look at this is using a window which
20 \ uses a fixed width font and is at least this wide:
22 \<------------------------------------------------------------------------------------------------------------------------>
24 \ Secondly make sure TABS are set to 8 characters. The following should be a vertical
25 \ line. If not, sort out your tabs.
31 \ Thirdly I assume that your screen is at least 50 characters high.
33 \ START OF FORTH CODE ----------------------------------------------------------------------
35 \ We've now reached the stage where the FORTH system is running and self-hosting. All further
36 \ words can be written as FORTH itself, including words like IF, THEN, .", etc which in most
37 \ languages would be considered rather fundamental.
39 \ Some notes about the code:
41 \ I use indenting to show structure. The amount of whitespace has no meaning to FORTH however
42 \ except that you must use at least one whitespace character between words, and words themselves
43 \ cannot contain whitespace.
45 \ FORTH is case-sensitive. Use capslock!
47 \ The primitive word /MOD (DIVMOD) leaves both the quotient and the remainder on the stack. (On
48 \ i386, the idivl instruction gives both anyway). Now we can define the / and MOD in terms of /MOD
49 \ and a few other primitives.
53 \ Define some character constants
55 : BL 32 ; \ BL (BLank) is a standard FORTH word for space.
57 \ CR prints a carriage return
60 \ SPACE prints a space
63 \ The 2... versions of the standard operators work on pairs of stack entries. They're not used
64 \ very commonly so not really worth writing in assembler. Here is how they are defined in FORTH.
68 \ More standard FORTH words.
72 \ NEGATE leaves the negative of a number on the stack.
75 \ Standard words for booleans.
80 \ LITERAL takes whatever is on the stack and compiles LIT <foo>
83 , \ compile the literal itself (from the stack)
86 \ Now we can use [ and ] to insert literals which are calculated at compile time. (Recall that
87 \ [ and ] are the FORTH words which switch into and out of immediate mode.)
88 \ Within definitions, use [ ... ] LITERAL anywhere that '...' is a constant expression which you
89 \ would rather only compute once (at compile time, rather than calculating it each time your word runs).
91 [ \ go into immediate mode (temporarily)
92 CHAR : \ push the number 58 (ASCII code of colon) on the parameter stack
93 ] \ go back to compile mode
94 LITERAL \ compile LIT 58 as the definition of ':' word
97 \ A few more character constants defined the same way as above.
98 : ';' [ CHAR ; ] LITERAL ;
99 : '(' [ CHAR ( ] LITERAL ;
100 : ')' [ CHAR ) ] LITERAL ;
101 : '"' [ CHAR " ] LITERAL ;
102 : 'A' [ CHAR A ] LITERAL ;
103 : '0' [ CHAR 0 ] LITERAL ;
104 : '-' [ CHAR - ] LITERAL ;
105 : '.' [ CHAR . ] LITERAL ;
107 \ While compiling, '[COMPILE] word' compiles 'word' if it would otherwise be IMMEDIATE.
108 : [COMPILE] IMMEDIATE
109 WORD \ get the next word
110 FIND \ find it in the dictionary
111 >CFA \ get its codeword
115 \ RECURSE makes a recursive call to the current word that is being compiled.
117 \ Normally while a word is being compiled, it is marked HIDDEN so that references to the
118 \ same word within are calls to the previous definition of the word. However we still have
119 \ access to the word which we are currently compiling through the LATEST pointer so we
120 \ can use that to compile a recursive call.
122 LATEST @ \ LATEST points to the word being compiled at the moment
123 >CFA \ get the codeword
127 \ CONTROL STRUCTURES ----------------------------------------------------------------------
129 \ So far we have defined only very simple definitions. Before we can go further, we really need to
130 \ make some control structures, like IF ... THEN and loops. Luckily we can define arbitrary control
131 \ structures directly in FORTH.
133 \ Please note that the control structures as I have defined them here will only work inside compiled
134 \ words. If you try to type in expressions using IF, etc. in immediate mode, then they won't work.
135 \ Making these work in immediate mode is left as an exercise for the reader.
137 \ condition IF true-part THEN rest
138 \ -- compiles to: --> condition 0BRANCH OFFSET true-part rest
139 \ where OFFSET is the offset of 'rest'
140 \ condition IF true-part ELSE false-part THEN
141 \ -- compiles to: --> condition 0BRANCH OFFSET true-part BRANCH OFFSET2 false-part rest
142 \ where OFFSET if the offset of false-part and OFFSET2 is the offset of rest
144 \ IF is an IMMEDIATE word which compiles 0BRANCH followed by a dummy offset, and places
145 \ the address of the 0BRANCH on the stack. Later when we see THEN, we pop that address
146 \ off the stack, calculate the offset, and back-fill the offset.
148 ' 0BRANCH , \ compile 0BRANCH
149 HERE @ \ save location of the offset on the stack
150 0 , \ compile a dummy offset
155 HERE @ SWAP - \ calculate the offset from the address saved on the stack
156 SWAP ! \ store the offset in the back-filled location
160 ' BRANCH , \ definite branch to just over the false-part
161 HERE @ \ save location of the offset on the stack
162 0 , \ compile a dummy offset
163 SWAP \ now back-fill the original (IF) offset
164 DUP \ same as for THEN word above
169 \ BEGIN loop-part condition UNTIL
170 \ -- compiles to: --> loop-part condition 0BRANCH OFFSET
171 \ where OFFSET points back to the loop-part
172 \ This is like do { loop-part } while (condition) in the C language
174 HERE @ \ save location on the stack
178 ' 0BRANCH , \ compile 0BRANCH
179 HERE @ - \ calculate the offset from the address saved on the stack
180 , \ compile the offset here
183 \ BEGIN loop-part AGAIN
184 \ -- compiles to: --> loop-part BRANCH OFFSET
185 \ where OFFSET points back to the loop-part
186 \ In other words, an infinite loop which can only be returned from with EXIT
188 ' BRANCH , \ compile BRANCH
189 HERE @ - \ calculate the offset back
190 , \ compile the offset here
193 \ BEGIN condition WHILE loop-part REPEAT
194 \ -- compiles to: --> condition 0BRANCH OFFSET2 loop-part BRANCH OFFSET
195 \ where OFFSET points back to condition (the beginning) and OFFSET2 points to after the whole piece of code
196 \ So this is like a while (condition) { loop-part } loop in the C language
198 ' 0BRANCH , \ compile 0BRANCH
199 HERE @ \ save location of the offset2 on the stack
200 0 , \ compile a dummy offset2
204 ' BRANCH , \ compile BRANCH
205 SWAP \ get the original offset (from BEGIN)
206 HERE @ - , \ and compile it after BRANCH
208 HERE @ SWAP - \ calculate the offset2
209 SWAP ! \ and back-fill it in the original location
212 \ UNLESS is the same as IF but the test is reversed.
214 \ Note the use of [COMPILE]: Since IF is IMMEDIATE we don't want it to be executed while UNLESS
215 \ is compiling, but while UNLESS is running (which happens to be when whatever word using UNLESS is
216 \ being compiled -- whew!). So we use [COMPILE] to reverse the effect of marking IF as immediate.
217 \ This trick is generally used when we want to write our own control words without having to
218 \ implement them all in terms of the primitives 0BRANCH and BRANCH, but instead reusing simpler
219 \ control words like (in this instance) IF.
221 ' NOT , \ compile NOT (to reverse the test)
222 [COMPILE] IF \ continue by calling the normal IF
225 \ COMMENTS ----------------------------------------------------------------------
227 \ FORTH allows ( ... ) as comments within function definitions. This works by having an IMMEDIATE
228 \ word called ( which just drops input characters until it hits the corresponding ).
230 1 \ allowed nested parens by keeping track of depth
232 KEY \ read next character
233 DUP '(' = IF \ open paren?
234 DROP \ drop the open paren
237 ')' = IF \ close paren?
241 DUP 0= UNTIL \ continue until we reach matching close paren, depth 0
242 DROP \ drop the depth counter
246 From now on we can use ( ... ) for comments.
248 STACK NOTATION ----------------------------------------------------------------------
250 In FORTH style we can also use ( ... -- ... ) to show the effects that a word has on the
251 parameter stack. For example:
253 ( n -- ) means that the word consumes an integer (n) from the parameter stack.
254 ( b a -- c ) means that the word uses two integers (a and b, where a is at the top of stack)
255 and returns a single integer (c).
256 ( -- ) means the word has no effect on the stack
259 ( Some more complicated stack examples, showing the stack notation. )
260 : NIP ( x y -- y ) SWAP DROP ;
261 : TUCK ( x y -- y x y ) DUP ROT ;
262 : PICK ( x_u ... x_1 x_0 u -- x_u ... x_1 x_0 x_u )
263 1+ ( add one because of 'u' on the stack )
264 4 * ( multiply by the word size )
265 DSP@ + ( add to the stack pointer )
269 ( With the looping constructs, we can now write SPACES, which writes n spaces to stdout. )
272 DUP 0> ( while n > 0 )
274 SPACE ( print a space )
275 1- ( until we count down to 0 )
280 ( Standard words for manipulating BASE. )
281 : DECIMAL ( -- ) 10 BASE ! ;
282 : HEX ( -- ) 16 BASE ! ;
285 PRINTING NUMBERS ----------------------------------------------------------------------
287 The standard FORTH word . (DOT) is very important. It takes the number at the top
288 of the stack and prints it out. However first I'm going to implement some lower-level
291 U.R ( u width -- ) which prints an unsigned number, padded to a certain width
292 U. ( u -- ) which prints an unsigned number
293 .R ( n width -- ) which prints a signed number, padded to a certain width.
297 will print out these characters:
298 <space> <space> - 1 2 3
300 In other words, the number padded left to a certain number of characters.
302 The full number is printed even if it is wider than width, and this is what allows us to
303 define the ordinary functions U. and . (we just set width to zero knowing that the full
304 number will be printed anyway).
306 Another wrinkle of . and friends is that they obey the current base in the variable BASE.
307 BASE can be anything in the range 2 to 36.
309 While we're defining . &c we can also define .S which is a useful debugging tool. This
310 word prints the current stack (non-destructively) from top to bottom.
313 ( This is the underlying recursive definition of U. )
315 BASE @ /MOD ( width rem quot )
316 ?DUP IF ( if quotient <> 0 then )
317 RECURSE ( print the quotient )
320 ( print the remainder )
322 '0' ( decimal digits 0..9 )
324 10 - ( hex and beyond digits A..Z )
332 FORTH word .S prints the contents of the stack. It doesn't alter the stack.
333 Very useful for debugging.
336 DSP@ ( get current stack pointer )
340 DUP @ U. ( print the stack element )
347 ( This word returns the width (in characters) of an unsigned number in the current base )
348 : UWIDTH ( u -- width )
349 BASE @ / ( rem quot )
350 ?DUP IF ( if quotient <> 0 then )
351 RECURSE 1+ ( return 1+recursive call )
360 UWIDTH ( width u uwidth )
361 -ROT ( u uwidth width )
362 SWAP - ( u width-uwidth )
363 ( At this point if the requested width is narrower, we'll have a negative number on the stack.
364 Otherwise the number on the stack is the number of spaces to print. But SPACES won't print
365 a negative number of spaces anyway, so it's now safe to call SPACES ... )
367 ( ... and then call the underlying implementation of U. )
372 .R prints a signed number, padded to a certain width. We can't just print the sign
373 and call U.R because we want the sign to be next to the number ('-123' instead of '- 123').
379 1 ( save a flag to remember that it was negative | width n 1 )
388 SWAP ( flag width u )
389 DUP ( flag width u u )
390 UWIDTH ( flag width u uwidth )
391 -ROT ( flag u uwidth width )
392 SWAP - ( flag u width-uwidth )
397 IF ( was it negative? print the - character )
404 ( Finally we can define word . in terms of .R, with a trailing space. )
407 ( The real U., note the trailing space. )
410 ( ? fetches the integer at an address and prints it. )
411 : ? ( addr -- ) @ . ;
413 ( c a b WITHIN returns true if a <= c and c < b )
429 ( DEPTH returns the depth of the stack. )
432 4- ( adjust because S0 was on the stack when we pushed DSP )
436 ALIGNED takes an address and rounds it up (aligns it) to the next 4 byte boundary.
438 : ALIGNED ( addr -- addr )
439 3 + 3 INVERT AND ( (addr+3) & ~3 )
443 ALIGN aligns the HERE pointer, so the next word appended will be aligned properly.
445 : ALIGN HERE @ ALIGNED HERE ! ;
448 STRINGS ----------------------------------------------------------------------
450 S" string" is used in FORTH to define strings. It leaves the address of the string and
451 its length on the stack, (length at the top of stack). The space following S" is the normal
452 space between FORTH words and is not a part of the string.
454 This is tricky to define because it has to do different things depending on whether
455 we are compiling or in immediate mode. (Thus the word is marked IMMEDIATE so it can
456 detect this and do different things).
458 In compile mode we append
459 LITSTRING <string length> <string rounded up 4 bytes>
460 to the current word. The primitive LITSTRING does the right thing when the current
463 In immediate mode there isn't a particularly good place to put the string, but in this
464 case we put the string at HERE (but we _don't_ change HERE). This is meant as a temporary
465 location, likely to be overwritten soon after.
467 ( C, appends a byte to the current compiled word. )
469 HERE @ C! ( store the character in the compiled image )
470 1 HERE +! ( increment HERE pointer by 1 byte )
473 : S" IMMEDIATE ( -- addr len )
474 STATE @ IF ( compiling? )
475 ' LITSTRING , ( compile LITSTRING )
476 HERE @ ( save the address of the length word on the stack )
477 0 , ( dummy length - we don't know what it is yet )
479 KEY ( get next character of the string )
482 C, ( copy character )
484 DROP ( drop the double quote character at the end )
485 DUP ( get the saved address of the length word )
486 HERE @ SWAP - ( calculate the length )
487 4- ( subtract 4 (because we measured from the start of the length word) )
488 SWAP ! ( and back-fill the length location )
489 ALIGN ( round up to next multiple of 4 bytes for the remaining code )
490 ELSE ( immediate mode )
491 HERE @ ( get the start address of the temporary space )
496 OVER C! ( save next character )
497 1+ ( increment address )
499 DROP ( drop the final " character )
500 HERE @ - ( calculate the length )
501 HERE @ ( push the start address )
507 ." is the print string operator in FORTH. Example: ." Something to print"
508 The space after the operator is the ordinary space required between words and is not
509 a part of what is printed.
511 In immediate mode we just keep reading characters and printing them until we get to
512 the next double quote.
514 In compile mode we use S" to store the string, then add TELL afterwards:
515 LITSTRING <string length> <string rounded up to 4 bytes> TELL
517 It may be interesting to note the use of [COMPILE] to turn the call to the immediate
518 word S" into compilation of that word. It compiles it into the definition of .",
519 not into the definition of the word being compiled when this is running (complicated
522 : ." IMMEDIATE ( -- )
523 STATE @ IF ( compiling? )
524 [COMPILE] S" ( read the string, and compile LITSTRING, etc. )
525 ' TELL , ( compile the final TELL )
527 ( In immediate mode, just read characters and print them until we get
528 to the ending double quote. )
532 DROP ( drop the double quote character )
533 EXIT ( return from this function )
541 CONSTANTS AND VARIABLES ----------------------------------------------------------------------
543 In FORTH, global constants and variables are defined like this:
545 10 CONSTANT TEN when TEN is executed, it leaves the integer 10 on the stack
546 VARIABLE VAR when VAR is executed, it leaves the address of VAR on the stack
548 Constants can be read but not written, eg:
552 You can read a variable (in this example called VAR) by doing:
554 VAR @ leaves the value of VAR on the stack
555 VAR @ . CR prints the value of VAR
556 VAR ? CR same as above, since ? is the same as @ .
558 and update the variable by doing:
560 20 VAR ! sets VAR to 20
562 Note that variables are uninitialised (but see VALUE later on which provides initialised
563 variables with a slightly simpler syntax).
565 How can we define the words CONSTANT and VARIABLE?
567 The trick is to define a new word for the variable itself (eg. if the variable was called
568 'VAR' then we would define a new word called VAR). This is easy to do because we exposed
569 dictionary entry creation through the CREATE word (part of the definition of : above).
570 A call to WORD [TEN] CREATE (where [TEN] means that "TEN" is the next word in the input)
571 leaves the dictionary entry:
576 +---------+---+---+---+---+
577 | LINK | 3 | T | E | N |
578 +---------+---+---+---+---+
581 For CONSTANT we can continue by appending DOCOL (the codeword), then LIT followed by
582 the constant itself and then EXIT, forming a little word definition that returns the
585 +---------+---+---+---+---+------------+------------+------------+------------+
586 | LINK | 3 | T | E | N | DOCOL | LIT | 10 | EXIT |
587 +---------+---+---+---+---+------------+------------+------------+------------+
590 Notice that this word definition is exactly the same as you would have got if you had
593 Note for people reading the code below: DOCOL is a constant word which we defined in the
594 assembler part which returns the value of the assembler symbol of the same name.
597 WORD ( get the name (the name follows CONSTANT) )
598 CREATE ( make the dictionary entry )
599 DOCOL , ( append DOCOL (the codeword field of this word) )
600 ' LIT , ( append the codeword LIT )
601 , ( append the value on the top of the stack )
602 ' EXIT , ( append the codeword EXIT )
606 VARIABLE is a little bit harder because we need somewhere to put the variable. There is
607 nothing particularly special about the user memory (the area of memory pointed to by HERE
608 where we have previously just stored new word definitions). We can slice off bits of this
609 memory area to store anything we want, so one possible definition of VARIABLE might create
612 +--------------------------------------------------------------+
615 +---------+---------+---+---+---+---+------------+------------+---|--------+------------+
616 | <var> | LINK | 3 | V | A | R | DOCOL | LIT | <addr var> | EXIT |
617 +---------+---------+---+---+---+---+------------+------------+------------+------------+
620 where <var> is the place to store the variable, and <addr var> points back to it.
622 To make this more general let's define a couple of words which we can use to allocate
623 arbitrary memory from the user memory.
625 First ALLOT, where n ALLOT allocates n bytes of memory. (Note when calling this that
626 it's a very good idea to make sure that n is a multiple of 4, or at least that next time
627 a word is compiled that HERE has been left as a multiple of 4).
629 : ALLOT ( n -- addr )
630 HERE @ SWAP ( here n )
631 HERE +! ( adds n to HERE, after this the old value of HERE is still on the stack )
635 Second, CELLS. In FORTH the phrase 'n CELLS ALLOT' means allocate n integers of whatever size
636 is the natural size for integers on this machine architecture. On this 32 bit machine therefore
637 CELLS just multiplies the top of stack by 4.
639 : CELLS ( n -- n ) 4 * ;
642 So now we can define VARIABLE easily in much the same way as CONSTANT above. Refer to the
643 diagram above to see what the word that this creates will look like.
646 1 CELLS ALLOT ( allocate 1 cell of memory, push the pointer to this memory )
647 WORD CREATE ( make the dictionary entry (the name follows VARIABLE) )
648 DOCOL , ( append DOCOL (the codeword field of this word) )
649 ' LIT , ( append the codeword LIT )
650 , ( append the pointer to the new memory )
651 ' EXIT , ( append the codeword EXIT )
655 VALUES ----------------------------------------------------------------------
657 VALUEs are like VARIABLEs but with a simpler syntax. You would generally use them when you
658 want a variable which is read often, and written infrequently.
660 20 VALUE VAL creates VAL with initial value 20
661 VAL pushes the value directly on the stack
662 30 TO VAL updates VAL, setting it to 30
664 Notice that 'VAL' on its own doesn't return the address of the value, but the value itself,
665 making values simpler and more obvious to use than variables (no indirection through '@').
666 The price is a more complicated implementation, although despite the complexity there is no
667 performance penalty at runtime.
669 A naive implementation of 'TO' would be quite slow, involving a dictionary search each time.
670 But because this is FORTH we have complete control of the compiler so we can compile TO more
671 efficiently, turning:
675 and calculating <addr> (the address of the value) at compile time.
677 Now this is the clever bit. We'll compile our value like this:
679 +---------+---+---+---+---+------------+------------+------------+------------+
680 | LINK | 3 | V | A | L | DOCOL | LIT | <value> | EXIT |
681 +---------+---+---+---+---+------------+------------+------------+------------+
684 where <value> is the actual value itself. Note that when VAL executes, it will push the
685 value on the stack, which is what we want.
687 But what will TO use for the address <addr>? Why of course a pointer to that <value>:
689 code compiled - - - - --+------------+------------+------------+-- - - - -
690 by TO VAL | LIT | <addr> | ! |
691 - - - - --+------------+-----|------+------------+-- - - - -
694 +---------+---+---+---+---+------------+------------+------------+------------+
695 | LINK | 3 | V | A | L | DOCOL | LIT | <value> | EXIT |
696 +---------+---+---+---+---+------------+------------+------------+------------+
699 In other words, this is a kind of self-modifying code.
701 (Note to the people who want to modify this FORTH to add inlining: values defined this
702 way cannot be inlined).
705 WORD CREATE ( make the dictionary entry (the name follows VALUE) )
706 DOCOL , ( append DOCOL )
707 ' LIT , ( append the codeword LIT )
708 , ( append the initial value )
709 ' EXIT , ( append the codeword EXIT )
712 : TO IMMEDIATE ( n -- )
713 WORD ( get the name of the value )
714 FIND ( look it up in the dictionary )
715 >DFA ( get a pointer to the first data field (the 'LIT') )
716 4+ ( increment to point at the value )
717 STATE @ IF ( compiling? )
718 ' LIT , ( compile LIT )
719 , ( compile the address of the value )
721 ELSE ( immediate mode )
722 ! ( update it straightaway )
726 ( x +TO VAL adds x to VAL )
728 WORD ( get the name of the value )
729 FIND ( look it up in the dictionary )
730 >DFA ( get a pointer to the first data field (the 'LIT') )
731 4+ ( increment to point at the value )
732 STATE @ IF ( compiling? )
733 ' LIT , ( compile LIT )
734 , ( compile the address of the value )
735 ' +! , ( compile +! )
736 ELSE ( immediate mode )
737 +! ( update it straightaway )
742 PRINTING THE DICTIONARY ----------------------------------------------------------------------
744 ID. takes an address of a dictionary entry and prints the word's name.
746 For example: LATEST @ ID. would print the name of the last word that was defined.
749 4+ ( skip over the link pointer )
750 DUP C@ ( get the flags/length byte )
751 F_LENMASK AND ( mask out the flags - just want the length )
754 DUP 0> ( length > 0? )
756 SWAP 1+ ( addr len -- len addr+1 )
757 DUP C@ ( len addr -- len addr char | get the next character)
758 EMIT ( len addr char -- len addr | and print it)
759 SWAP 1- ( len addr -- addr len-1 | subtract one from length )
761 2DROP ( len addr -- )
765 'WORD word FIND ?HIDDEN' returns true if 'word' is flagged as hidden.
767 'WORD word FIND ?IMMEDIATE' returns true if 'word' is flagged as immediate.
770 4+ ( skip over the link pointer )
771 C@ ( get the flags/length byte )
772 F_HIDDEN AND ( mask the F_HIDDEN flag and return it (as a truth value) )
775 4+ ( skip over the link pointer )
776 C@ ( get the flags/length byte )
777 F_IMMED AND ( mask the F_IMMED flag and return it (as a truth value) )
781 WORDS prints all the words defined in the dictionary, starting with the word defined most recently.
782 However it doesn't print hidden words.
784 The implementation simply iterates backwards from LATEST using the link pointers.
787 LATEST @ ( start at LATEST dictionary entry )
789 ?DUP ( while link pointer is not null )
791 DUP ?HIDDEN NOT IF ( ignore hidden words )
792 DUP ID. ( but if not hidden, print the word )
795 @ ( dereference the link pointer - go to previous word )
801 FORGET ----------------------------------------------------------------------
803 So far we have only allocated words and memory. FORTH provides a rather primitive method
806 'FORGET word' deletes the definition of 'word' from the dictionary and everything defined
807 after it, including any variables and other memory allocated after.
809 The implementation is very simple - we look up the word (which returns the dictionary entry
810 address). Then we set HERE to point to that address, so in effect all future allocations
811 and definitions will overwrite memory starting at the word. We also need to set LATEST to
812 point to the previous word.
814 Note that you cannot FORGET built-in words (well, you can try but it will probably cause
817 XXX: Because we wrote VARIABLE to store the variable in memory allocated before the word,
818 in the current implementation VARIABLE FOO FORGET FOO will leak 1 cell of memory.
821 WORD FIND ( find the word, gets the dictionary entry address )
822 DUP @ LATEST ! ( set LATEST to point to the previous word )
823 HERE ! ( and store HERE with the dictionary address )
827 DUMP ----------------------------------------------------------------------
829 DUMP is used to dump out the contents of memory, in the 'traditional' hexdump format.
831 Notice that the parameters to DUMP (address, length) are compatible with string words
834 : DUMP ( addr len -- )
835 BASE @ ROT ( save the current BASE at the bottom of the stack )
836 HEX ( and switch the hexadecimal mode )
839 DUP 0> ( while len > 0 )
841 OVER 8 U.R ( print the address )
844 ( print up to 16 words on this line )
845 2DUP ( addr len addr len )
846 1- 15 AND 1+ ( addr len addr linelen )
848 DUP 0> ( while linelen > 0 )
850 SWAP ( addr len linelen addr )
851 DUP C@ ( addr len linelen addr byte )
852 2 .R SPACE ( print the byte )
853 1+ SWAP 1- ( addr len linelen addr -- addr len addr+1 linelen-1 )
857 ( print the ASCII equivalents )
858 2DUP 1- 15 AND 1+ ( addr len addr linelen )
860 DUP 0> ( while linelen > 0)
862 SWAP ( addr len linelen addr )
863 DUP C@ ( addr len linelen addr byte )
864 DUP 32 128 WITHIN IF ( 32 <= c < 128? )
869 1+ SWAP 1- ( addr len linelen addr -- addr len addr+1 linelen-1 )
874 DUP 1- 15 AND 1+ ( addr len linelen )
875 DUP ( addr len linelen linelen )
876 ROT ( addr linelen len linelen )
877 - ( addr linelen len-linelen )
878 ROT ( len-linelen addr linelen )
879 + ( len-linelen addr+linelen )
880 SWAP ( addr-linelen len-linelen )
883 2DROP ( restore stack )
884 BASE ! ( restore saved BASE )
888 CASE ----------------------------------------------------------------------
890 CASE...ENDCASE is how we do switch statements in FORTH. There is no generally
891 agreed syntax for this, so I've gone for the syntax mandated by the ISO standard
894 ( some value on the stack )
902 The CASE statement tests the value on the stack by comparing it for equality with
903 test1, test2, ..., testn and executes the matching piece of code within OF ... ENDOF.
904 If none of the test values match then the default case is executed. Inside the ... of
905 the default case, the value is still at the top of stack (it is implicitly DROP-ed
906 by ENDCASE). When ENDOF is executed it jumps after ENDCASE (ie. there is no "fall-through"
907 and no need for a break statement like in C).
909 The default case may be omitted. In fact the tests may also be omitted so that you
910 just have a default case, although this is probably not very useful.
912 An example (assuming that 'q', etc. are words which push the ASCII value of the letter
918 'q' OF 1 TO QUIT ENDOF
919 's' OF 1 TO SLEEP ENDOF
921 ." Sorry, I didn't understand key <" DUP EMIT ." >, try again." CR
924 (In some versions of FORTH, more advanced tests are supported, such as ranges, etc.
925 Other versions of FORTH need you to write OTHERWISE to indicate the default case.
926 As I said above, this FORTH tries to follow the ANS FORTH standard).
928 The implementation of CASE...ENDCASE is somewhat non-trivial. I'm following the
929 implementations from here:
930 http://www.uni-giessen.de/faq/archiv/forthfaq.case_endcase/msg00000.html
932 The general plan is to compile the code as a series of IF statements:
934 CASE (push 0 on the immediate-mode parameter stack)
935 test1 OF ... ENDOF test1 OVER = IF DROP ... ELSE
936 test2 OF ... ENDOF test2 OVER = IF DROP ... ELSE
937 testn OF ... ENDOF testn OVER = IF DROP ... ELSE
938 ... ( default case ) ...
939 ENDCASE DROP THEN [THEN [THEN ...]]
941 The CASE statement pushes 0 on the immediate-mode parameter stack, and that number
942 is used to count how many THEN statements we need when we get to ENDCASE so that each
943 IF has a matching THEN. The counting is done implicitly. If you recall from the
944 implementation above of IF, each IF pushes a code address on the immediate-mode stack,
945 and these addresses are non-zero, so by the time we get to ENDCASE the stack contains
946 some number of non-zeroes, followed by a zero. The number of non-zeroes is how many
947 times IF has been called, so how many times we need to match it with THEN.
949 This code uses [COMPILE] so that we compile calls to IF, ELSE, THEN instead of
950 actually calling them while we're compiling the words below.
952 As is the case with all of our control structures, they only work within word
953 definitions, not in immediate mode.
956 0 ( push 0 to mark the bottom of the stack )
960 ' OVER , ( compile OVER )
962 [COMPILE] IF ( compile IF )
963 ' DROP , ( compile DROP )
967 [COMPILE] ELSE ( ENDOF is the same as ELSE )
971 ' DROP , ( compile DROP )
973 ( keep compiling THEN until we get to our zero marker )
982 DECOMPILER ----------------------------------------------------------------------
984 CFA> is the opposite of >CFA. It takes a codeword and tries to find the matching
985 dictionary definition. (In truth, it works with any pointer into a word, not just
986 the codeword pointer, and this is needed to do stack traces).
988 In this FORTH this is not so easy. In fact we have to search through the dictionary
989 because we don't have a convenient back-pointer (as is often the case in other versions
990 of FORTH). Because of this search, CFA> should not be used when performance is critical,
991 so it is only used for debugging tools such as the decompiler and printing stack
994 This word returns 0 if it doesn't find a match.
997 LATEST @ ( start at LATEST dictionary entry )
999 ?DUP ( while link pointer is not null )
1001 2DUP SWAP ( cfa curr curr cfa )
1002 < IF ( current dictionary entry < cfa? )
1003 NIP ( leave curr dictionary entry on the stack )
1006 @ ( follow link pointer back )
1008 DROP ( restore stack )
1009 0 ( sorry, nothing found )
1013 SEE decompiles a FORTH word.
1015 We search for the dictionary entry of the word, then search again for the next
1016 word (effectively, the end of the compiled word). This results in two pointers:
1018 +---------+---+---+---+---+------------+------------+------------+------------+
1019 | LINK | 3 | T | E | N | DOCOL | LIT | 10 | EXIT |
1020 +---------+---+---+---+---+------------+------------+------------+------------+
1023 Start of word End of word
1025 With this information we can have a go at decompiling the word. We need to
1026 recognise "meta-words" like LIT, LITSTRING, BRANCH, etc. and treat those separately.
1029 WORD FIND ( find the dictionary entry to decompile )
1031 ( Now we search again, looking for the next word in the dictionary. This gives us
1032 the length of the word that we will be decompiling. (Well, mostly it does). )
1033 HERE @ ( address of the end of the last compiled word )
1034 LATEST @ ( word last curr )
1036 2 PICK ( word last curr word )
1037 OVER ( word last curr word curr )
1038 <> ( word last curr word<>curr? )
1039 WHILE ( word last curr )
1041 DUP @ ( word curr prev (which becomes: word last curr) )
1044 DROP ( at this point, the stack is: start-of-word end-of-word )
1045 SWAP ( end-of-word start-of-word )
1047 ( begin the definition with : NAME [IMMEDIATE] )
1048 ':' EMIT SPACE DUP ID. SPACE
1049 DUP ?IMMEDIATE IF ." IMMEDIATE " THEN
1051 >DFA ( get the data address, ie. points after DOCOL | end-of-word start-of-data )
1053 ( now we start decompiling until we hit the end of the word )
1057 DUP @ ( end start codeword )
1060 ' LIT OF ( is it LIT ? )
1061 4 + DUP @ ( get next word which is the integer constant )
1064 ' LITSTRING OF ( is it LITSTRING ? )
1065 [ CHAR S ] LITERAL EMIT '"' EMIT SPACE ( print S"<space> )
1066 4 + DUP @ ( get the length word )
1067 SWAP 4 + SWAP ( end start+4 length )
1068 2DUP TELL ( print the string )
1069 '"' EMIT SPACE ( finish the string with a final quote )
1070 + ALIGNED ( end start+4+len, aligned )
1071 4 - ( because we're about to add 4 below )
1073 ' 0BRANCH OF ( is it 0BRANCH ? )
1075 4 + DUP @ ( print the offset )
1079 ' BRANCH OF ( is it BRANCH ? )
1081 4 + DUP @ ( print the offset )
1085 ' ' OF ( is it ' (TICK) ? )
1086 [ CHAR ' ] LITERAL EMIT SPACE
1087 4 + DUP @ ( get the next codeword )
1088 CFA> ( and force it to be printed as a dictionary entry )
1091 ' EXIT OF ( is it EXIT? )
1092 ( We expect the last word to be EXIT, and if it is then we don't print it
1093 because EXIT is normally implied by ;. EXIT can also appear in the middle
1094 of words, and then it needs to be printed. )
1095 2DUP ( end start end start )
1096 4 + ( end start end start+4 )
1097 <> IF ( end start | we're not at the end )
1102 DUP ( in the default case we always need to DUP before using )
1103 CFA> ( look up the codeword to get the dictionary entry )
1104 ID. SPACE ( and print it )
1112 2DROP ( restore stack )
1116 EXECUTION TOKENS ----------------------------------------------------------------------
1118 Standard FORTH defines a concept called an 'execution token' (or 'xt') which is very
1119 similar to a function pointer in C. We map the execution token to a codeword address.
1121 execution token of DOUBLE is the address of this codeword
1124 +---------+---+---+---+---+---+---+---+---+------------+------------+------------+------------+
1125 | LINK | 6 | D | O | U | B | L | E | 0 | DOCOL | DUP | + | EXIT |
1126 +---------+---+---+---+---+---+---+---+---+------------+------------+------------+------------+
1129 There is one assembler primitive for execution tokens, EXECUTE ( xt -- ), which runs them.
1131 You can make an execution token for an existing word the long way using >CFA,
1132 ie: WORD [foo] FIND >CFA will push the xt for foo onto the stack where foo is the
1133 next word in input. So a very slow way to run DOUBLE might be:
1136 : SLOW WORD FIND >CFA EXECUTE ;
1137 5 SLOW DOUBLE . CR \ prints 10
1139 We also offer a simpler and faster way to get the execution token of any word FOO:
1143 (Exercises for readers: (1) What is the difference between ['] FOO and ' FOO?
1144 (2) What is the relationship between ', ['] and LIT?)
1146 More useful is to define anonymous words and/or to assign xt's to variables.
1148 To define an anonymous word (and push its xt on the stack) use :NONAME ... ; as in this
1151 :NONAME ." anon word was called" CR ; \ pushes xt on the stack
1152 DUP EXECUTE EXECUTE \ executes the anon word twice
1154 Stack parameters work as expected:
1156 :NONAME ." called with parameter " . CR ;
1158 10 SWAP EXECUTE \ prints 'called with parameter 10'
1159 20 SWAP EXECUTE \ prints 'called with parameter 20'
1161 Notice that the above code has a memory leak: the anonymous word is still compiled
1162 into the data segment, so even if you lose track of the xt, the word continues to
1163 occupy memory. A good way to keep track of the xt and thus avoid the memory leak is
1164 to assign it to a CONSTANT, VARIABLE or VALUE:
1167 :NONAME ." anon word was called" CR ; TO ANON
1171 Another use of :NONAME is to create an array of functions which can be called quickly
1172 (think: fast switch statement). This example is adapted from the ANS FORTH standard:
1174 10 CELLS ALLOT CONSTANT CMD-TABLE
1175 : SET-CMD CELLS CMD-TABLE + ! ;
1176 : CALL-CMD CELLS CMD-TABLE + @ EXECUTE ;
1178 :NONAME ." alternate 0 was called" CR ; 0 SET-CMD
1179 :NONAME ." alternate 1 was called" CR ; 1 SET-CMD
1181 :NONAME ." alternate 9 was called" CR ; 9 SET-CMD
1188 0 0 CREATE ( create a word with no name - we need a dictionary header because ; expects it )
1189 HERE @ ( current HERE value is the address of the codeword, ie. the xt )
1190 DOCOL , ( compile DOCOL (the codeword) )
1191 ] ( go into compile mode )
1195 ' LIT , ( compile LIT )
1199 EXCEPTIONS ----------------------------------------------------------------------
1201 Amazingly enough, exceptions can be implemented directly in FORTH, in fact rather easily.
1203 The general usage is as follows:
1205 : FOO ( n -- ) THROW ;
1208 25 ['] FOO CATCH \ execute 25 FOO, catching any exception
1210 ." called FOO and it threw exception number: "
1212 DROP \ we have to drop the argument of FOO (25)
1215 \ prints: called FOO and it threw exception number: 25
1217 CATCH runs an execution token and detects whether it throws any exception or not. The
1218 stack signature of CATCH is rather complicated:
1220 ( a_n-1 ... a_1 a_0 xt -- r_m-1 ... r_1 r_0 0 ) if xt did NOT throw an exception
1221 ( a_n-1 ... a_1 a_0 xt -- ?_n-1 ... ?_1 ?_0 e ) if xt DID throw exception 'e'
1223 where a_i and r_i are the (arbitrary number of) argument and return stack contents
1224 before and after xt is EXECUTEd. Notice in particular the case where an exception
1225 is thrown, the stack pointer is restored so that there are n of _something_ on the
1226 stack in the positions where the arguments a_i used to be. We don't really guarantee
1227 what is on the stack -- perhaps the original arguments, and perhaps other nonsense --
1228 it largely depends on the implementation of the word that was executed.
1230 THROW, ABORT and a few others throw exceptions.
1232 Exception numbers are non-zero integers. By convention the positive numbers can be used
1233 for app-specific exceptions and the negative numbers have certain meanings defined in
1234 the ANS FORTH standard. (For example, -1 is the exception thrown by ABORT).
1236 0 THROW does nothing. This is the stack signature of THROW:
1239 ( * e -- ?_n-1 ... ?_1 ?_0 e ) the stack is restored to the state from the corresponding CATCH
1241 The implementation hangs on the definitions of CATCH and THROW and the state shared
1244 Up to this point, the return stack has consisted merely of a list of return addresses,
1245 with the top of the return stack being the return address where we will resume executing
1246 when the current word EXITs. However CATCH will push a more complicated 'exception stack
1247 frame' on the return stack. The exception stack frame records some things about the
1248 state of execution at the time that CATCH was called.
1250 When called, THROW walks up the return stack (the process is called 'unwinding') until
1251 it finds the exception stack frame. It then uses the data in the exception stack frame
1252 to restore the state allowing execution to continue after the matching CATCH. (If it
1253 unwinds the stack and doesn't find the exception stack frame then it prints a message
1254 and drops back to the prompt, which is also normal behaviour for so-called 'uncaught
1257 This is what the exception stack frame looks like. (As is conventional, the return stack
1258 is shown growing downwards from higher to lower memory addresses).
1260 +------------------------------+
1261 | return address from CATCH | Notice this is already on the
1262 | | return stack when CATCH is called.
1263 +------------------------------+
1264 | original parameter stack |
1266 +------------------------------+ ^
1267 | exception stack marker | |
1268 | (EXCEPTION-MARKER) | | Direction of stack
1269 +------------------------------+ | unwinding by THROW.
1273 The EXCEPTION-MARKER marks the entry as being an exception stack frame rather than an
1274 ordinary return address, and it is this which THROW "notices" as it is unwinding the
1275 stack. (If you want to implement more advanced exceptions such as TRY...WITH then
1276 you'll need to use a different value of marker if you want the old and new exception stack
1277 frame layouts to coexist).
1279 What happens if the executed word doesn't throw an exception? It will eventually
1280 return and call EXCEPTION-MARKER, so EXCEPTION-MARKER had better do something sensible
1281 without us needing to modify EXIT. This nicely gives us a suitable definition of
1282 EXCEPTION-MARKER, namely a function that just drops the stack frame and itself
1283 returns (thus "returning" from the original CATCH).
1285 One thing to take from this is that exceptions are a relatively lightweight mechanism
1290 RDROP ( drop the original parameter stack pointer )
1291 0 ( there was no exception, this is the normal return path )
1294 : CATCH ( xt -- exn? )
1295 DSP@ 4+ >R ( save parameter stack pointer (+4 because of xt) on the return stack )
1296 ' EXCEPTION-MARKER 4+ ( push the address of the RDROP inside EXCEPTION-MARKER ... )
1297 >R ( ... on to the return stack so it acts like a return address )
1298 EXECUTE ( execute the nested function )
1302 ?DUP IF ( only act if the exception code <> 0 )
1303 RSP@ ( get return stack pointer )
1305 DUP R0 4- < ( RSP < R0 )
1307 DUP @ ( get the return stack entry )
1308 ' EXCEPTION-MARKER 4+ = IF ( found the EXCEPTION-MARKER on the return stack )
1309 4+ ( skip the EXCEPTION-MARKER on the return stack )
1310 RSP! ( restore the return stack pointer )
1312 ( Restore the parameter stack. )
1313 DUP DUP DUP ( reserve some working space so the stack for this word
1314 doesn't coincide with the part of the stack being restored )
1315 R> ( get the saved parameter stack pointer | n dsp )
1316 4- ( reserve space on the stack to store n )
1317 SWAP OVER ( dsp n dsp )
1318 ! ( write n on the stack )
1319 DSP! EXIT ( restore the parameter stack pointer, immediately exit )
1324 ( No matching catch - print a message and restart the INTERPRETer. )
1343 ( Print a stack trace by walking up the return stack. )
1345 RSP@ ( start at caller of this function )
1347 DUP R0 4- < ( RSP < R0 )
1349 DUP @ ( get the return stack entry )
1351 ' EXCEPTION-MARKER 4+ OF ( is it the exception stack frame? )
1353 4+ DUP @ U. ( print saved stack pointer )
1358 CFA> ( look up the codeword to get the dictionary entry )
1359 ?DUP IF ( and print it )
1360 2DUP ( dea addr dea )
1361 ID. ( print word from dictionary entry )
1362 [ CHAR + ] LITERAL EMIT
1363 SWAP >DFA 4+ - . ( print offset )
1366 4+ ( move up the stack )
1373 C STRINGS ----------------------------------------------------------------------
1375 FORTH strings are represented by a start address and length kept on the stack or in memory.
1377 Most FORTHs don't handle C strings, but we need them in order to access the process arguments
1378 and environment left on the stack by the Linux kernel, and to make some system calls.
1380 Operation Input Output FORTH word Notes
1381 ----------------------------------------------------------------------
1383 Create FORTH string addr len S" ..."
1385 Create C string c-addr Z" ..."
1387 C -> FORTH c-addr addr len DUP STRLEN
1389 FORTH -> C addr len c-addr CSTRING Allocated in a temporary buffer, so
1390 should be consumed / copied immediately.
1391 FORTH string should not contain NULs.
1393 For example, DUP STRLEN TELL prints a C string.
1397 Z" .." is like S" ..." except that the string is terminated by an ASCII NUL character.
1399 To make it more like a C string, at runtime Z" just leaves the address of the string
1400 on the stack (not address & length as with S"). To implement this we need to add the
1401 extra NUL to the string and also a DROP instruction afterwards. Apart from that the
1402 implementation just a modified S".
1405 STATE @ IF ( compiling? )
1406 ' LITSTRING , ( compile LITSTRING )
1407 HERE @ ( save the address of the length word on the stack )
1408 0 , ( dummy length - we don't know what it is yet )
1410 KEY ( get next character of the string )
1413 HERE @ C! ( store the character in the compiled image )
1414 1 HERE +! ( increment HERE pointer by 1 byte )
1416 0 HERE @ C! ( add the ASCII NUL byte )
1418 DROP ( drop the double quote character at the end )
1419 DUP ( get the saved address of the length word )
1420 HERE @ SWAP - ( calculate the length )
1421 4- ( subtract 4 (because we measured from the start of the length word) )
1422 SWAP ! ( and back-fill the length location )
1423 ALIGN ( round up to next multiple of 4 bytes for the remaining code )
1424 ' DROP , ( compile DROP (to drop the length) )
1425 ELSE ( immediate mode )
1426 HERE @ ( get the start address of the temporary space )
1431 OVER C! ( save next character )
1432 1+ ( increment address )
1434 DROP ( drop the final " character )
1435 0 SWAP C! ( store final ASCII NUL )
1436 HERE @ ( push the start address )
1440 : STRLEN ( str -- len )
1441 DUP ( save start address )
1443 DUP C@ 0<> ( zero byte found? )
1448 SWAP - ( calculate the length )
1451 : CSTRING ( addr len -- c-addr )
1452 SWAP OVER ( len saddr len )
1453 HERE @ SWAP ( len saddr daddr len )
1456 HERE @ + ( daddr+len )
1457 0 SWAP C! ( store terminating NUL char )
1459 HERE @ ( push start address )
1463 THE ENVIRONMENT ----------------------------------------------------------------------
1465 Linux makes the process arguments and environment available to us on the stack.
1467 The top of stack pointer is saved by the early assembler code when we start up in the FORTH
1468 variable S0, and starting at this pointer we can read out the command line arguments and the
1471 Starting at S0, S0 itself points to argc (the number of command line arguments).
1473 S0+4 points to argv[0], S0+8 points to argv[1] etc up to argv[argc-1].
1475 argv[argc] is a NULL pointer.
1477 After that the stack contains environment variables, a set of pointers to strings of the
1478 form NAME=VALUE and on until we get to another NULL pointer.
1480 The first word that we define, ARGC, pushes the number of command line arguments (note that
1481 as with C argc, this includes the name of the command).
1488 n ARGV gets the nth command line argument.
1490 For example to print the command name you would do:
1493 : ARGV ( n -- str u )
1494 1+ CELLS S0 @ + ( get the address of argv[n] entry )
1495 @ ( get the address of the string )
1496 DUP STRLEN ( and get its length / turn it into a FORTH string )
1500 ENVIRON returns the address of the first environment string. The list of strings ends
1501 with a NULL pointer.
1503 For example to print the first string in the environment you could do:
1504 ENVIRON @ DUP STRLEN TELL
1506 : ENVIRON ( -- addr )
1507 ARGC ( number of command line parameters on the stack to skip )
1508 2 + ( skip command line count and NULL pointer after the command line args )
1509 CELLS ( convert to an offset )
1510 S0 @ + ( add to base stack address )
1514 SYSTEM CALLS AND FILES ----------------------------------------------------------------------
1516 Miscellaneous words related to system calls, and standard access to files.
1519 ( BYE exits by calling the Linux exit(2) syscall. )
1521 0 ( return code (0) )
1522 SYS_EXIT ( system call number )
1527 UNUSED returns the number of cells remaining in the user memory (data segment).
1529 For our implementation we will use Linux brk(2) system call to find out the end
1530 of the data segment and subtract HERE from it.
1532 : GET-BRK ( -- brkpoint )
1533 0 SYS_BRK SYSCALL1 ( call brk(0) )
1537 GET-BRK ( get end of data segment according to the kernel )
1538 HERE @ ( get current position in data segment )
1540 4 / ( returns number of cells )
1544 MORECORE increases the data segment by the specified number of (4 byte) cells.
1546 NB. The number of cells requested should normally be a multiple of 1024. The
1547 reason is that Linux can't extend the data segment by less than a single page
1548 (4096 bytes or 1024 cells).
1550 This FORTH doesn't automatically increase the size of the data segment "on demand"
1551 (ie. when , (COMMA), ALLOT, CREATE, and so on are used). Instead the programmer
1552 needs to be aware of how much space a large allocation will take, check UNUSED, and
1553 call MORECORE if necessary. A simple programming exercise is to change the
1554 implementation of the data segment so that MORECORE is called automatically if
1555 the program needs more memory.
1557 : BRK ( brkpoint -- )
1561 : MORECORE ( cells -- )
1566 Standard FORTH provides some simple file access primitives which we model on
1567 top of Linux syscalls.
1569 The main complication is converting FORTH strings (address & length) into C
1570 strings for the Linux kernel.
1572 Notice there is no buffering in this implementation.
1575 : R/O ( -- fam ) O_RDONLY ;
1576 : R/W ( -- fam ) O_RDWR ;
1578 : OPEN-FILE ( addr u fam -- fd 0 (if successful) | c-addr u fam -- fd errno (if there was an error) )
1580 CSTRING ( fam cstring )
1581 SYS_OPEN SYSCALL2 ( open (filename, flags) )
1583 DUP 0< IF ( errno? )
1590 : CREATE-FILE ( addr u fam -- fd 0 (if successful) | c-addr u fam -- fd errno (if there was an error) )
1594 CSTRING ( fam cstring )
1595 420 ROT ( 0644 fam cstring )
1596 SYS_OPEN SYSCALL3 ( open (filename, flags|O_TRUNC|O_CREAT, 0644) )
1598 DUP 0< IF ( errno? )
1605 : CLOSE-FILE ( fd -- 0 (if successful) | fd -- errno (if there was an error) )
1610 : READ-FILE ( addr u fd -- u2 0 (if successful) | addr u fd -- 0 0 (if EOF) | addr u fd -- u2 errno (if error) )
1611 ROT SWAP -ROT ( u addr fd )
1615 DUP 0< IF ( errno? )
1623 PERROR prints a message for an errno, similar to C's perror(3) but we don't have the extensive
1624 list of strerror strings available, so all we can do is print the errno.
1626 : PERROR ( errno addr u -- )
1634 NOTES ----------------------------------------------------------------------
1636 DOES> isn't possible to implement with this FORTH because we don't have a separate
1641 WELCOME MESSAGE ----------------------------------------------------------------------
1643 Print the version and OK prompt.
1647 S" TEST-MODE" FIND NOT IF
1648 ." JONESFORTH VERSION " VERSION . CR
1649 UNUSED . ." CELLS REMAINING" CR