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https://github.com/hsoft/collapseos.git
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forth: simplify execution model and handle literals better
This scheme of "when we handle line-by-line, compile one word at a time then execute" so that we could allow words like "CREATE" to call "readword" before continuing was a bad scheme. It made things like branching outside of a colon definition impossible. This commit implement a new "litWord". When an undefined word is encountered at compile time, it is included as-is in a string literal word. It is at run time that we decide what to do with it.
This commit is contained in:
Virgil Dupras
parent
5cadde557c
commit
03e529b762
@ -71,10 +71,27 @@ numberWord:
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NUMBER:
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.dw numberWord
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; Similarly to numberWord, this is not a real word, but a string literal.
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; Instead of being followed by a 2 bytes number, it's followed by a
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; null-terminated string. This is not expected to be called in a regular
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; context. Only words expecting those literals will look for them. This is why
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; the litWord triggers abort.
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litWord:
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call popRS
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call intoHL
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call printstr ; let's print the word before abort.
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ld hl, .msg
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call printstr
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jp abort
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.msg:
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.db "undefined word", 0
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LIT:
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.dw litWord
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; ( R:I -- )
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EXIT:
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.db "EXIT", 0, 0, 0, 0
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.db ";"
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.fill 7
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.dw 0
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.dw nativeWord
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; When we call the EXIT word, we have to do a "double exit" because our current
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@ -88,7 +105,7 @@ exit:
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call popRS
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; We have a pointer to a word
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push hl \ pop iy
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jr compiledWord
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jp compiledWord
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; ( R:I -- )
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QUIT:
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@ -96,31 +113,29 @@ QUIT:
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.dw EXIT
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.dw nativeWord
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quit:
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ld hl, FLAGS
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set FLAG_QUITTING, (hl)
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jr exit
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jp forthRdLine
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ABORT:
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.db "ABORT", 0, 0, 0
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.dw QUIT
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.dw nativeWord
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abort:
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; Reinitialize PS (RS is reinitialized in forthInterpret
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ld sp, (INITIAL_SP)
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ld hl, .msg
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call printstr
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call printcrlf
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jr quit
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.msg:
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.db " err", 0
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jp forthRdLine
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BYE:
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.db "BYE"
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.fill 5
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.dw ABORT
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.dw nativeWord
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ld hl, FLAGS
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set FLAG_ENDPGM, (hl)
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jp exit
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; Goodbye Forth! Before we go, let's restore the stack
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ld sp, (INITIAL_SP)
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; unwind stack underflow buffer
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pop af \ pop af \ pop af
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; success
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xor a
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ret
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; ( c -- )
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EMIT:
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@ -155,36 +170,44 @@ DEFINE:
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.dw EXECUTE
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.dw nativeWord
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call entryhead
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jp nz, quit
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ld de, compiledWord
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ld (hl), e
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inc hl
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ld (hl), d
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inc hl
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push hl \ pop iy
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; At this point, we've processed the name literal following the ':'.
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; What's next? We have, in IP, a pointer to words that *have already
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; been compiled by INTERPRET*. All those bytes will be copied as-is.
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; All we need to do is to know how many bytes to copy. To do so, we
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; skip compwords until EXIT is reached.
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ld (HERE), hl ; where we write compwords.
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; Let's save old RS TOS
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ld e, (ix)
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ld d, (ix+1)
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.loop:
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call readword
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jr nz, .end
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call .issemicol
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jr z, .end
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call compile
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jp nz, quit
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call RSIsEXIT
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jr z, .loopend
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call compSkip
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jr .loop
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.end:
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; end chain with EXIT
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ld hl, EXIT+CODELINK_OFFSET
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call wrCompHL
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ld (HERE), iy
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.loopend:
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; At this point, RS' TOS points to EXIT compword. We'll copy it too.
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; We'll use LDIR. BC will be RSTOP-OLDRSTOP+2
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ld l, (ix)
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ld h, (ix+1)
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inc hl \ inc hl ; our +2
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or a ; clear carry
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sbc hl, de
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ld b, h
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ld c, l
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; BC has proper count
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ex de, hl ; HL is our source (old RS' TOS)
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ld de, (HERE) ; and DE is our dest
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ldir ; go!
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; HL has our new RS' TOS
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ld (ix), l
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ld (ix+1), h
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ld (HERE), de ; update HERE
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jp exit
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.issemicol:
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ld a, (hl)
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cp ';'
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ret nz
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inc hl
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ld a, (hl)
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dec hl
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or a
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ret
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DOES:
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.db "DOES>", 0, 0, 0
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@ -226,22 +249,17 @@ INTERPRET:
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.dw KEY
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.dw nativeWord
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interpret:
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call readword
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jp nz, quit
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ld iy, COMPBUF
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.loop:
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call readword
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jr nz, .end
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call compile
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jp nz, .notfound
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ld hl, EXIT+CODELINK_OFFSET
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ld (iy), l
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ld (iy+1), h
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jr .loop
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.end:
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ld hl, QUIT+CODELINK_OFFSET
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call wrCompHL
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ld iy, COMPBUF
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jp compiledWord
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.notfound:
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ld hl, .msg
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call printstr
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jp quit
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.msg:
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.db "not found", 0
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CREATE:
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.db "CREATE", 0, 0
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@ -454,4 +472,3 @@ CONSTANT:
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.dw DOES+CODELINK_OFFSET
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.dw FETCH+CODELINK_OFFSET
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.dw EXIT+CODELINK_OFFSET
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@ -17,7 +17,8 @@ DOES>: Used inside a colon definition that itself uses CREATE, DOES> transforms
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*** Native Words ***
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: x ... ; -- Define a new word
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: x ... -- Define a new word
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; R:I -- Exit a colon definition
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. n -- Print n in its decimal form
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@ a -- n Set n to value at address a
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! n a -- Store n in address a
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@ -30,7 +31,6 @@ DOES> -- See description at top of file
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DUP a -- a a
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EMIT c -- Spit char c to stdout
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EXECUTE a -- Execute word at addr a
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EXIT R:I -- Exit a colon definition
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HERE -- a Push HERE's address
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QUIT R:drop -- Return to interpreter promp immediately
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KEY -- c Get char c from stdin
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@ -7,47 +7,17 @@
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.equ NAMELEN 8
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; Offset of the code link relative to the beginning of the word
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.equ CODELINK_OFFSET 10
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; When set, the interpreter should abort parsing of current line and return to
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; prompt.
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.equ FLAG_QUITTING 0
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; When set, the interpreter should quit
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.equ FLAG_ENDPGM 1
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; *** Variables ***
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.equ INITIAL_SP FORTH_RAMSTART
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.equ CURRENT @+2
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.equ HERE @+2
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.equ INPUTPOS @+2
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.equ FLAGS @+2
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; Buffer where we compile the current input line. Same size as STDIO_BUFSIZE.
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.equ COMPBUF @+1
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.equ COMPBUF @+2
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.equ FORTH_RAMEND @+0x40
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; *** Code ***
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MAIN:
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.dw compiledWord
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.dw INTERPRET+CODELINK_OFFSET
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.dw CHKEND
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; If FLAG_ENDPGM is set, stop the program, else, tweak the RS so that we loop.
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CHKEND:
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.dw nativeWord
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ld hl, FLAGS
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bit FLAG_ENDPGM, (hl)
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jr nz, .endpgm
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; not quitting program, are we supposed to continue parsing line?
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ld hl, FLAGS
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bit FLAG_QUITTING, (hl)
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jr nz, forthRdLine
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; Not quitting line either.
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jr forthInterpret
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.endpgm:
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ld sp, (INITIAL_SP)
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; restore stack
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pop af \ pop af \ pop af
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xor a
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ret
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forthMain:
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; STACK OVERFLOW PROTECTION:
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; To avoid having to check for stack underflow after each pop operation
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@ -62,16 +32,14 @@ forthMain:
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ld hl, FORTH_RAMEND
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ld (HERE), hl
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forthRdLine:
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xor a
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ld (FLAGS), a
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ld hl, msgOk
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call printstr
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call printcrlf
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call stdioReadLine
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ld (INPUTPOS), hl
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forthInterpret:
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ld ix, RS_ADDR
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ld iy, MAIN
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ld ix, RS_ADDR-2 ; -2 because we inc-before-push
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ld iy, INTERPRET+CODELINK_OFFSET
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jp executeCodeLink
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msgOk:
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.db " ok", 0
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@ -3,25 +3,26 @@
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; PS is the most frequently used. However, this causes a problem with routine
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; calls: because in Forth, the stack isn't balanced within each call, our return
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; offset, when placed by a CALL, messes everything up. This is one of the
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; reasons why we need stack management routines below.
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; reasons why we need stack management routines below. IX always points to RS'
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; Top Of Stack (TOS)
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;
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; This return stack contain "Interpreter pointers", that is a pointer to the
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; address of a word, as seen in a compiled list of words.
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; Push value HL to RS
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pushRS:
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inc ix
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inc ix
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ld (ix), l
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inc ix
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ld (ix), h
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inc ix
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ld (ix+1), h
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ret
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; Pop RS' TOS to HL
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popRS:
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dec ix
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ld h, (ix)
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dec ix
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ld l, (ix)
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ld h, (ix+1)
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dec ix
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dec ix
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ret
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; Verifies that SP is within bounds. If it's not, call ABORT
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@ -43,6 +43,126 @@ readword:
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inc a ; unset Z
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ret
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RSIsDE:
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push hl
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ld l, (ix)
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ld h, (ix+1)
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ld a, (hl)
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cp e
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jr nz, .end ; no
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inc hl
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ld a, (hl)
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cp d ; Z has our answer
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.end:
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pop hl
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ret
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; Is RS' TOS pointing to a NUMBER word?
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; Z if yes, NZ if no.
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RSIsNUMBER:
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push de
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ld de, NUMBER
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call RSIsDE
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pop de
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ret
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; Is RS' TOS pointing to a LIT word?
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; Z if yes, NZ if no.
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RSIsLIT:
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push de
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ld de, LIT
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call RSIsDE
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pop de
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ret
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; Is RS' TOS pointing to EXIT?
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; Z if yes, NZ if no.
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RSIsEXIT:
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push de
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ld de, EXIT+CODELINK_OFFSET
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call RSIsDE
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pop de
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ret
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; Skip the compword where RS' TOS is currently pointing. If it's a regular word,
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; it's easy: we inc by 2. If it's a NUMBER, we inc by 4. If it's a LIT, we skip
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; to after null-termination.
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compSkip:
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push hl
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ld l, (ix)
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ld h, (ix+1)
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; At the minimum, we skip by 2
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inc hl \ inc hl
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call RSIsNUMBER
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jr z, .isNum
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call RSIsLIT
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jr nz, .end ; A word
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; We have a literal
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call strskip
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inc hl ; byte after word termination
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jr .end
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.isNum:
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; skip by 4
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inc hl \ inc hl
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.end:
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; HL is good, write it to RS
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ld (ix), l
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ld (ix+1), h
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pop hl
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ret
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; Checks RS' TOS and, if it points to a string literal (LIT), makes HL point
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; to it and advance IP to byte following null-termination.
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; If it doesn't, things get interesting: If it's a word reference, then it's
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; not an invalid literal. For example, one could want to redefine an existing
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; word. So in that case, we'll copy the word's name on the pad (it might not be
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; null-terminated) and set HL to point to it.
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; How do we know that our reference is a word reference (it could be, for
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; example, a NUMBER reference)? We check that its address is more than QUIT, the
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; second word in our dict. We don't accept EXIT because it's the termination
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; word. Yeah, it means that ";" can't be overridden...
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; If name can't be read, we abort
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readCompWord:
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; In all cases, we want RS' TOS in HL. Let's get it now.
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ld l, (ix)
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ld h, (ix+1)
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call RSIsLIT
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jr nz, .notLIT
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; RS TOS is a LIT, make HL point to string, then skip this RS compword.
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inc hl \ inc hl ; HL now points to string itself
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jr compSkip
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.notLIT:
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; Alright, not a literal, but is it a word? If it's not a number, then
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; it's a word.
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call RSIsNUMBER
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jr z, .notWord
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; Not a number, then it's a word. Copy word to pad and point to it.
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call intoHL
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or a ; clear carry
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ld de, CODELINK_OFFSET
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sbc hl, de
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; That's our return value
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push hl ; --> lvl 1
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; HL now points to word offset, let'd copy it to pad
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ex de, hl
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call pad
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ex de, hl
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ld bc, NAMELEN
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ldir
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; null-terminate
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xor a
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ld (de), a
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call compSkip
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pop hl ; <-- lvl 1
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ret
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.notWord:
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ld hl, .msg
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call printstr
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jp abort
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.msg:
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.db "word expected", 0
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; For DE pointing to a dict entry, set DE to point to the previous entry.
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; Z is set if DE point to 0 (no entry). NZ if not.
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prev:
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@ -84,38 +204,48 @@ wrCompHL:
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; Compile word string at (HL) and write down its compiled version in IY,
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; advancing IY to the byte next to the last written byte.
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; Set Z on success, unset on failure.
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compile:
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call find
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jr nz, .maybeNum
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ret nz
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; DE is a word offset, we need a code link
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ld hl, CODELINK_OFFSET
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add hl, de
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xor a ; set Z
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jr wrCompHL
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.maybeNum:
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push hl ; --> lvl 1. save string addr
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call parseLiteral
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ret nz
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jr nz, .undef
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pop hl ; <-- lvl 1
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; a valid number!
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ld hl, NUMBER
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call wrCompHL
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ex de, hl ; number in HL
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jr wrCompHL
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ret z
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; unknown name
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ld hl, .msg
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call printstr
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jp abort
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.msg:
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.db "unknown name", 0
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.undef:
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; When encountering an undefined word during compilation, we spit a
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; reference to litWord, followed by the null-terminated word.
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; This way, if a preceding word expect a string literal, it will read it
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; by calling readCompWord, and if it doesn't, the routine will be
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; called, triggering an abort.
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ld hl, LIT
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call wrCompHL
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pop hl ; <-- lvl 1. recall string addr
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.writeLit:
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ld a, (hl)
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ld (iy), a
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inc hl
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inc iy
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or a
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jr nz, .writeLit
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ret
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; Spit name + prev in (HERE) and adjust (HERE) and (CURRENT)
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; HL points to new (HERE)
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; Set Z if name could be read, NZ if not
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entryhead:
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call readword
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ret nz
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call readCompWord
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call printstr
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ld de, (HERE)
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call strcpy
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ex de, hl ; (HERE) now in HL
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