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forth: Replace "SKIP?" with "(?br)"
There is an alternate git history where I continued the Forth-ification of words, including "SKIP?", but that was a bad idea: because that word was written by flow control immediates, I stepped into quicksands where stability became necessary in z80c.fs and I couldn't gracefully get out of it. I'm stepping back and take this opportunity to replace the shoddy SKIP? algo with a more straightforward (?br) implementation. (br) and (?br) will always stay in boot code where it's easier manage a stable ABI.
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@ -2,17 +2,17 @@
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: -^ SWAP - ;
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: [ INTERPRET 1 FLAGS ! ; IMMEDIATE
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: ] R> DROP ;
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: LIT [ JTBL 26 + LITN ] , ;
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: LIT JTBL 26 + , ;
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: LITS LIT SCPY ;
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: LIT< WORD LITS ; IMMEDIATE
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: _err LIT< word-not-found (print) ABORT ;
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: ' WORD (find) SKIP? _err ;
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: ['] WORD (find) SKIP? _err LITN ; IMMEDIATE
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: ' WORD (find) NOT (?br) [ 4 , ] _err ;
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: ['] ' LITN ; IMMEDIATE
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: COMPILE ' LITN ['] , , ; IMMEDIATE
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: [COMPILE] ' , ; IMMEDIATE
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: BEGIN H@ ; IMMEDIATE
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: AGAIN COMPILE (br) H@ - , ; IMMEDIATE
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: UNTIL COMPILE SKIP? COMPILE (br) H@ - , ; IMMEDIATE
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: UNTIL COMPILE (?br) H@ - , ; IMMEDIATE
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: ( BEGIN LIT< ) WORD SCMP NOT UNTIL ; IMMEDIATE
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( Hello, hello, krkrkrkr... do you hear me?
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Ah, voice at last! Some lines above need comments
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@ -29,8 +29,7 @@
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: ALLOT HERE +! ;
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: IF ( -- a | a: br cell addr )
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COMPILE SKIP? ( if true, don't branch )
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COMPILE (br)
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COMPILE (?br)
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H@ ( push a )
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2 ALLOT ( br cell allot )
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; IMMEDIATE
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@ -73,7 +72,7 @@
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the RS )
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: LOOP
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COMPILE R> 1 LITN COMPILE + COMPILE DUP COMPILE >R
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COMPILE I' COMPILE = COMPILE SKIP? COMPILE (br)
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COMPILE I' COMPILE = COMPILE (?br)
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H@ - ,
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COMPILE R> COMPILE DROP COMPILE R> COMPILE DROP
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; IMMEDIATE
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@ -73,10 +73,9 @@ Note about flow words: flow words can only be used in definitions. In the
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INTERPRET loop, they don't have the desired effect because each word from the
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input stream is executed immediately. In this context, branching doesn't work.
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(fbr) -- Branches forward by the number specified in its
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atom's cell.
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(bbr) -- Branches backward by the number specified in its
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atom's cell.
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(br) -- Branches by the number specified in the 2 following
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bytes. Can be negative.
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(?br) f -- Branch if f is false.
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[ -- Begin interetative mode. In a definition, words
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between here and "]" will be executed instead of
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compiled.
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@ -92,9 +91,6 @@ INTERPRET -- Get a line from stdin, compile it in tmp memory,
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then execute the compiled contents.
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QUIT R:drop -- Return to interpreter prompt immediately
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RECURSE R:I -- R:I-2 Run the current word again.
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SKIP? f -- If f is true, skip the execution of the next atom.
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Use this right before ";" and you're gonna have a
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bad time.
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THEN I:a -- *I* Set branching cell at a.
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UNTIL f -- *I* Jump backwards to BEGIN if f is *false*.
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@ -670,61 +670,28 @@ BR:
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ld (IP), hl
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jp next
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; Skip the compword where HL 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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.db "SKIP?"
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.fill 72
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.db "(?br)"
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.dw $-BR
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.db 5
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CSKIP:
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CBR:
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.dw nativeWord
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pop hl
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call chkPS
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ld a, h
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or l
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jp z, next ; False, do nothing.
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ld hl, (IP)
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ld de, NUMBER
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call .HLPointsDE
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jr z, .isNum
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ld de, BR
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call .HLPointsDE
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jr z, .isNum
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ld de, LIT
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call .HLPointsDE
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jr nz, .isWord
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; We have a literal
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inc hl \ inc hl
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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
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inc hl
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; continue to isWord
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.isWord:
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; skip by 2
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inc hl \ inc hl
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.end:
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ld (IP), hl
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jp z, BR+2 ; False, branch
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; True, skip next 2 bytes and don't branch
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ld hl, IP
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inc (hl)
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inc (hl)
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jp next
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; Sets Z if (HL) == E and (HL+1) == D
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.HLPointsDE:
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ld a, (hl)
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cp e
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ret nz ; no
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inc hl
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ld a, (hl)
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dec hl
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cp d ; Z has our answer
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ret
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.fill 45
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.fill 18
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.db ","
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.dw $-CSKIP
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.dw $-CBR
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.db 1
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WR:
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.dw nativeWord
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@ -1046,3 +1013,5 @@ CMP:
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.db "_bend"
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.dw $-CMP
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.db 5
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; Offset: 06ee
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.out $
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@ -54,7 +54,7 @@
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( This is only the "early parser" in earlier stages. No need
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for an abort message )
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: (parse)
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(parsed) SKIP? _c ABORT
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(parsed) NOT IF _c ABORT THEN
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;
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( a -- )
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@ -75,10 +75,10 @@
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;
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: (parse) ( a -- n )
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(parsec) NOT SKIP? EXIT
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(parseh) NOT SKIP? EXIT
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(parseb) NOT SKIP? EXIT
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(parsed) NOT SKIP? EXIT
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(parsec) IF EXIT THEN
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(parseh) IF EXIT THEN
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(parseb) IF EXIT THEN
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(parsed) IF EXIT THEN
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( nothing works )
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ABORT" unknown word! "
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;
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@ -4,6 +4,6 @@
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: fail SPC ." failed" LF 1 1 PC! BYE ;
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: # SKIP? fail SPC ." pass" LF ;
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: # IF SPC ." pass" LF ELSE fail THEN ;
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: #eq 2DUP SWAP . SPC '=' EMIT SPC . '?' EMIT = # ;
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