\ A sometimes minimal FORTH compiler and tutorial for Linux / i386 systems. -*- asm -*-
\ By Richard W.M. Jones <rich@annexia.org> http://annexia.org/forth
\ This is PUBLIC DOMAIN (see public domain release statement below).
-\ $Id: jonesforth.f,v 1.10 2007-09-29 16:06:27 rich Exp $
+\ $Id: jonesforth.f,v 1.11 2007-09-29 23:13:45 rich Exp $
\
\ The first part of this tutorial is in jonesforth.S. Get if from http://annexia.org/forth
\
: MOD /MOD DROP ;
\ Define some character constants
-: '\n' 10 ;
-: 'SPACE' 32 ;
+: '\n' 10 ;
+: BL 32 ; \ BL (BLank) is a standard FORTH word for space.
\ CR prints a carriage return
: CR '\n' EMIT ;
\ SPACE prints a space
-: SPACE 'SPACE' EMIT ;
+: SPACE BL EMIT ;
\ DUP, DROP are defined in assembly for speed, but this is how you might define them
\ in FORTH. Notice use of the scratch variables _X and _Y.
( This is the underlying recursive definition of U. )
: U. ( u -- )
BASE @ /MOD ( width rem quot )
- DUP 0<> IF ( if quotient <> 0 then )
+ ?DUP IF ( if quotient <> 0 then )
RECURSE ( print the quotient )
- ELSE
- DROP ( drop the zero quotient )
THEN
( print the remainder )
( This word returns the width (in characters) of an unsigned number in the current base )
: UWIDTH ( u -- width )
BASE @ / ( rem quot )
- DUP 0<> IF ( if quotient <> 0 then )
+ ?DUP IF ( if quotient <> 0 then )
RECURSE 1+ ( return 1+recursive call )
ELSE
- DROP ( drop the zero quotient )
1 ( return 1 )
THEN
;
: WORDS
LATEST @ ( start at LATEST dictionary entry )
BEGIN
- DUP 0<> ( while link pointer is not null )
+ ?DUP ( while link pointer is not null )
WHILE
DUP ?HIDDEN NOT IF ( ignore hidden words )
DUP ID. ( but if not hidden, print the word )
SPACE
@ ( dereference the link pointer - go to previous word )
REPEAT
- DROP
CR
;
: CFA>
LATEST @ ( start at LATEST dictionary entry )
BEGIN
- DUP 0<> ( while link pointer is not null )
+ ?DUP ( while link pointer is not null )
WHILE
DUP >CFA ( cfa curr curr-cfa )
2 PICK ( cfa curr curr-cfa cfa )
THEN
@ ( follow link pointer back )
REPEAT
- 2DROP ( restore stack )
+ DROP ( restore stack )
0 ( sorry, nothing found )
;
." 0BRANCH ( "
4 + DUP @ ( print the offset )
.
- ')' EMIT SPACE
+ ." ) "
ENDOF
' BRANCH OF ( is it BRANCH ? )
." BRANCH ( "
4 + DUP @ ( print the offset )
.
- ')' EMIT SPACE
+ ." ) "
ENDOF
' ' OF ( is it ' (TICK) ? )
[ CHAR ' ] LITERAL EMIT SPACE
;
(
- DOES> ----------------------------------------------------------------------
-
- CREATE ... DOES> is a tricky construct allowing you to create words which create other words.
- For example CONSTANT (defined above) is a word which creates words, and it could have been
- written as follows:
-
- : CONSTANT CREATE DOCOL , , DOES> @ ;
-
- Even explaining what DOES> is supposed to do is tricky. It's possible that the implementation
- is easier to understand than the explanation.
-
- If we look at the definition of CONSTANT here, and remember that when it is called the value
- of the constant is on the stack and the name follows. So first CREATE makes the header of a
- new word with the name. Secondly the codeword is set to DOCOL. Thirdly , (COMMA) takes the
- value off the stack and adds it to the definition. At this point (just before executing DOES>)
- the word looks like this:
-
- ________ CREATE _______ _ DOCOL ,_ ____ , ___
- / \ / \ / \
- +---------+---+---+---+---+------------+------------+
- | LINK | 3 | T | E | N | DOCOL | 10 |
- +---------+---+---+---+---+------------+------------+
- ^ len codeword
- |
- LATEST
-
-
-)
-
-
-
-
-: DOES>
- R> LATEST @ >DFA !
-;
-
-(
C STRINGS ----------------------------------------------------------------------
FORTH strings are represented by a start address and length kept on the stack or in memory.
prints a C string).
)
+(
+ Z" .." is like S" ..." except that the string is terminated by an ASCII NUL character.
+
+ To make it more like a C string, at runtime Z" just leaves the address of the string
+ on the stack (not address & length as with S"). To implement this we need to add the
+ extra NUL to the string and also a DROP instruction afterwards. Apart from that the
+ implementation just a modified S".
+)
+: Z" IMMEDIATE
+ STATE @ IF ( compiling? )
+ ' LITSTRING , ( compile LITSTRING )
+ HERE @ ( save the address of the length word on the stack )
+ 0 , ( dummy length - we don't know what it is yet )
+ BEGIN
+ KEY ( get next character of the string )
+ DUP '"' <>
+ WHILE
+ HERE @ C! ( store the character in the compiled image )
+ 1 HERE +! ( increment HERE pointer by 1 byte )
+ REPEAT
+ 0 HERE @ C! ( add the ASCII NUL byte )
+ 1 HERE +!
+ DROP ( drop the double quote character at the end )
+ DUP ( get the saved address of the length word )
+ HERE @ SWAP - ( calculate the length )
+ 4- ( subtract 4 (because we measured from the start of the length word) )
+ SWAP ! ( and back-fill the length location )
+ ALIGN ( round up to next multiple of 4 bytes for the remaining code )
+ ' DROP , ( compile DROP (to drop the length) )
+ ELSE ( immediate mode )
+ HERE @ ( get the start address of the temporary space )
+ BEGIN
+ KEY
+ DUP '"' <>
+ WHILE
+ OVER C! ( save next character )
+ 1+ ( increment address )
+ REPEAT
+ DROP ( drop the final " character )
+ 0 SWAP C! ( store final ASCII NUL )
+ HERE @ ( push the start address )
+ THEN
+;
+
( STRLEN returns the length of a C string )
: STRLEN ( str -- len )
DUP ( save start address )
;
(
+ SYSTEM CALLS ----------------------------------------------------------------------
+
+ Some wrappers around Linux system calls
+)
+
+( BYE exits by calling the Linux exit(2) syscall. )
+: BYE ( -- )
+ 0
+ 0
+ 0 ( return code (0) )
+ SYS_EXIT ( system call number )
+ SYSCALL3
+;
+
+(
+ OPEN, CREAT and CLOSE are just like the Linux syscalls open(2), creat(2) and close(2).
+
+ Notice that they take C strings and may return error codes (-errno).
+)
+: OPEN ( mode flags c-pathname -- ret )
+ SYS_OPEN
+ SYSCALL3
+;
+
+: CREAT ( mode c-pathname -- ret )
+ 0 ROT
+ SYS_CREAT
+ SYSCALL3
+;
+
+: CLOSE ( fd -- ret )
+ 0 ROT 0 ROT
+ SYS_CLOSE
+ SYSCALL3
+;
+
+( READ and WRITE system calls. )
+: READ ( len buffer fd -- ret )
+ SYS_READ
+ SYSCALL3
+;
+
+: WRITE ( len buffer fd -- ret )
+ SYS_WRITE
+ SYSCALL3
+;
+
+(
ANS FORTH ----------------------------------------------------------------------
From this point we're trying to fill in the missing parts of the ISO standard, commonly
http://www.taygeta.com/forth/dpans.html
http://www.taygeta.com/forth/dpansf.htm (list of words)
)
-( BL pushes the ASCII character code of space on the stack. )
-: BL 32 ;
( C, writes a byte at the HERE pointer. )
: C, HERE @ C! 1 HERE +! ;
-( Finally print the welcome prompt. )
+
+
+
+
+
+
+(
+ NOTES ----------------------------------------------------------------------
+
+ DOES> isn't possible to implement with this FORTH because we don't have a separate
+ data pointer.
+)
+
+(
+ WELCOME MESSAGE ----------------------------------------------------------------------
+
+ Print the version and OK prompt.
+)
+
." JONESFORTH VERSION " VERSION . CR
." OK "
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