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forth: Forth-ify IF and ELSE
Now, I really need comments...
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@ -1,11 +1,15 @@
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: H HERE @ ;
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: -^ SWAP - ;
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: ? @ . ;
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: +! SWAP OVER @ + SWAP ! ;
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: ALLOT HERE +! ;
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: VARIABLE CREATE 2 ALLOT ;
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: CONSTANT CREATE HERE @ ! DOES> @ ;
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: , HERE @ ! 2 ALLOT ;
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: C, HERE @ C! 1 ALLOT ;
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: THEN DUP HERE @ SWAP - SWAP C! ; IMMEDIATE
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: CONSTANT CREATE H ! DOES> @ ;
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: , H ! 2 ALLOT ;
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: C, H C! 1 ALLOT ;
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: IF ['] (fbr?) , H 0 C, ; IMMEDIATE
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: THEN DUP H -^ SWAP C! ; IMMEDIATE
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: ELSE ['] (fbr) , 0 C, DUP H -^ SWAP C! H 1 - ; IMMEDIATE
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: NOT IF 0 ELSE 1 THEN ;
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: = CMP NOT ;
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: < CMP 0 1 - = ;
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@ -676,53 +676,8 @@ FBRC:
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jp exit
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; : IF ' (fbr?) , HERE @ 0 C, ; IMMEDIATE
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.db "IF"
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.fill 5
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.dw FBRC
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.db 1 ; IMMEDIATE
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IF:
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.dw nativeWord
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; Spit a conditional branching atom, followed by an empty 1b cell. Then,
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; push the address of that cell on the PS. ELSE or THEN will pick
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; them up and set the offset.
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ld hl, (HERE)
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ld de, FBRC
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call DEinHL
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push hl ; address of cell to fill
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inc hl ; empty 1b cell
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ld (HERE), hl
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jp exit
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.db "ELSE"
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.fill 3
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.dw IF
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.db 1 ; IMMEDIATE
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ELSE:
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.dw nativeWord
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; First, let's set IF's branching cell.
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pop de ; cell's address
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ld hl, (HERE)
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; also skip ELSE word.
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inc hl \ inc hl \ inc hl
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or a ; clear carry
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sbc hl, de ; HL now has relative offset
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ld a, l
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ld (de), a
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; Set IF's branching cell to current atom address and spit our own
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; uncondition branching cell, which will then be picked up by THEN.
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; First, let's spit our 4 bytes
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ld hl, (HERE)
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ld de, FBR
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call DEinHL
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push hl ; address of cell to fill
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inc hl ; empty 1b cell
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ld (HERE), hl
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jp exit
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.db "RECURSE"
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.dw ELSE
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.dw FBRC
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.db 0
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RECURSE:
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.dw nativeWord
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@ -77,11 +77,13 @@ C@ a -- c Set c to byte at address a
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C! c a -- Store byte c in address a
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CURRENT -- n Set n to wordref of last added entry.
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HERE -- a Push HERE's address
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H -- a HERE @
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*** Arithmetic ***
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+ a b -- c a + b -> c
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- a b -- c a - b -> c
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-^ a b -- c b - a -> c
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* a b -- c a * b -> c
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/ a b -- c a / b -> c
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