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https://github.com/hsoft/collapseos.git
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forth: change the whole execution model again
Things are better now, but immediates inside colons are broken. However, IF/THEN/ELSE are now immediates and it's much cleaner this way. Still, this commit has too much stuff in it, I need to commit, I don't want to lose this step.
This commit is contained in:
Virgil Dupras
parent
2ddca57f3f
commit
6757c097ea
@ -51,69 +51,31 @@ doesWord:
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push hl \ pop iy
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jr compiledWord
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; The IF word checks the stack for zero. If it's non-zero, it does nothing and
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; allow compiledWord to continue.
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; If it's zero, it tracksback RS, advance it until it finds a ELSE, a THEN, or
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; an EXIT (not supposed to happen unless the IF is misconstructed). Whether
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; it's a ELSE or THEN, the same thing happens: we resume execution after the
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; ELSE/THEN. If it's a EXIT, we simply execute it.
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ifWord:
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; This word is followed by a wordref to branch to. Set RS to that address.
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branchWord:
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ld l, (ix)
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ld h, (ix+1)
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call intoHL
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ld (ix), l
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ld (ix+1), h
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jp exit
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BRANCH:
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.dw branchWord
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; Conditional branch, only branch if TOS is zero
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cbranchWord:
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pop hl
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ld a, h
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or l
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jp nz, exit ; non-zero, continue
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; Zero, seek ELSE, THEN or EXIT. Continue to elseWord
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; If a ELSE word is executed, it means that the preceding IF had a non-zero
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; condition and continued execution. This means that upon encountering an ELSE,
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; we must search for a THEN or an EXIT.
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; To simplify implementation and share code with ifWord, we also match ELSE,
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; which is only possible in malformed construct. Therefore "IF ELSE ELSE" is
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; valid and interpreted as "IF ELSE THEN".
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elseWord:
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; to save processing, we test EXIT, ELSE and THEN in the order they
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; appear, address-wise. This way, we don't need to push/pop HL: we can
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; SUB the difference between the words and check for zeroes.
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call popRS
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; We need to save that IP somewhere. Let it be BC
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ld b, h
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ld c, l
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.loop:
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; Whether there's a match or not, we will resume the operation at IP+2,
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; which means that we have to increase BC anyways. Let's do it now.
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inc bc \ inc bc
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call intoHL
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or a ; clear carry
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ld de, EXIT
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sbc hl, de
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jp z, exit
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; Not EXIT, let's continue with ELSE. No carry possible because EXIT
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; is first word. No need to clear.
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ld de, ELSE-EXIT
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sbc hl, de
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jr c, .nomatch ; A word between EXIT and ELSE. No match.
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jr z, .match ; We have a ELSE
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; Let's try with THEN. Again, no carry possible, C cond was handled.
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ld de, THEN-ELSE
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sbc hl, de
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jr z, .match ; We have a THEN
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.nomatch:
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; Nothing matched, which means that we need to continue looking.
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; BC is already IP+2
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ld h, b
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ld l, c
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jr .loop
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.match:
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; Matched a ELSE or a THEN, which means we need to continue executing
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; word from IP+2, which is already in BC.
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push bc \ pop iy
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jp compiledWord
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; This word does nothing. It's never going to be executed unless the wordlist
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; is misconstructed.
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thenWord:
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jr z, branchWord
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; skip next 2 bytes
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call skipRS
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jp exit
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CBRANCH:
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.dw cbranchWord
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; This is not a word, but a number literal. This works a bit differently than
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; others: PF means nothing and the actual number is placed next to the
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; numberWord reference in the compiled word list. What we need to do to fetch
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@ -121,12 +83,14 @@ thenWord:
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; it to the Parameter stack and then push an increase Interpreter Pointer back
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; to RS.
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numberWord:
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call popRS
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ld l, (ix)
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ld h, (ix+1)
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ld e, (hl)
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inc hl
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ld d, (hl)
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inc hl
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call pushRS
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ld (ix), l
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ld (ix+1), h
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push de
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jp exit
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NUMBER:
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@ -186,6 +150,8 @@ abort:
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; Reinitialize PS (RS is reinitialized in forthInterpret
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ld sp, (INITIAL_SP)
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jp forthRdLine
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ABORTREF:
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.dw ABORT
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.db "BYE"
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.fill 5
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@ -290,7 +256,7 @@ DEFINE:
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jr nz, .notIMMED
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; Immediate word, we'll have to call it.
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; Before we make our call, let's save our current HL/DE position
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ld (HERE), de
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ld (CMPDST), de
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ld e, (hl)
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inc hl
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ld d, (hl)
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@ -329,7 +295,7 @@ DEFINE:
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; recall old HL / DE values
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ld l, (ix)
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ld h, (ix+1)
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ld de, (HERE)
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ld de, (CMPDST)
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; continue!
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jr .loop
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@ -374,18 +340,12 @@ IMMEDIATE:
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.dw IMMEDIATE
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LITERAL:
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.dw nativeWord
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ld hl, (HERE)
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ld hl, (CMPDST)
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ld de, NUMBER
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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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call DEinHL
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pop de ; number from stack
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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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ld (HERE), hl
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call DEinHL
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ld (CMPDST), hl
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jp exit
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; ( -- c )
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@ -400,27 +360,9 @@ KEY:
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push hl
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jp exit
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.db "INTERPR"
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.db 0
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.dw KEY
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INTERPRET:
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.dw nativeWord
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interpret:
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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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jr .loop
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.end:
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ld hl, QUIT
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call wrCompHL
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ld iy, COMPBUF
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jp compiledWord
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.db "CREATE"
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.fill 2
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.dw INTERPRET
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.dw KEY
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CREATE:
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.dw nativeWord
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call entryhead
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@ -607,22 +549,61 @@ CMP:
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jp exit
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.db "IF"
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.fill 6
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.fill 5
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.db 1 ; IMMEDIATE
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.dw CMP
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IF:
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.dw ifWord
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.dw nativeWord
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; Spit a conditional branching atom, followed by 2 empty bytes. Then,
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; push the address of those 2 bytes on the PS. ELSE or THEN will pick
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; them up and set their own address in those 2 bytes.
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ld hl, (CMPDST)
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ld de, CBRANCH
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call DEinHL
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push hl ; address of cell to fill
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; For now, let's fill it with a reference to ABORT in case we have a
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; malformed construct
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ld de, ABORTREF
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call DEinHL
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ld (CMPDST), hl
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jp exit
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.db "ELSE"
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.fill 4
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.fill 3
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.db 1 ; IMMEDIATE
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.dw IF
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ELSE:
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.dw elseWord
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.dw nativeWord
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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, (CMPDST)
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ld de, BRANCH
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call DEinHL
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push hl ; address of cell to fill
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ld de, ABORTREF
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call DEinHL
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ld (CMPDST), hl
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; We've spit our ELSE bytes, but we haven't updated our IF's forward
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; branching cell. That cell's address is currently at (SP-2). Let's do
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; some stack-fu to get it.
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ex de, hl ; value to write now in DE
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pop hl
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ex (sp), hl ; IF's cell's address now in HL
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call DEinHL
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jp exit
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.db "THEN"
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.fill 4
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.fill 3
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.db 1 ; IMMEDIATE
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.dw ELSE
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THEN:
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.dw thenWord
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.dw nativeWord
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; See comments in IF and ELSE
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pop hl ; where to put our own address
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ld de, (CMPDST) ; that's our branching address
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call DEinHL
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jp exit
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.db "RECURSE"
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.db 0
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@ -755,5 +736,3 @@ LATEST:
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.dw 1
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.dw EQ
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.dw EXIT
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;
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@ -12,11 +12,35 @@
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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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; Pointer to where we currently are in the interpretation of the current line.
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.equ INPUTPOS @+2
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; Pointer to where compiling words should output. During interpret, it's a
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; moving target in (COMPBUF). During DEFINE, it's (HERE).
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.equ CMPDST @+2
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; Buffer where we compile the current input line. Same size as STDIO_BUFSIZE.
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.equ COMPBUF @+2
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.equ FORTH_RAMEND @+0x40
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; EXECUTION MODEL
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; After having read a line through stdioReadLine, we want to interpret it. As
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; a general rule, we go like this:
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;
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; 1. read single word from line
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; 2. compile word to atom
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; 3. execute atom
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; 4. goto 1
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;
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; During step 3, it's possible that atom read from input, so INPUTPOS might
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; have moved between 3 and 4.
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;
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; Because the Parameter Stack uses PS, we can't just go around calling routines:
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; This messes with the PS. This is why we almost always jump (unless our call
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; doesn't involve Forth words in any way).
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;
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; This presents a challenge for our interpret loop because step 4, "goto 1"
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; isn't obvious. To be able to do that, we must push a "return routine" to the
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; Return Stack before step 3.
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; *** Code ***
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forthMain:
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; STACK OVERFLOW PROTECTION:
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@ -36,10 +60,70 @@ forthRdLine:
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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-2 ; -2 because we inc-before-push
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ld iy, INTERPRET
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ld (INPUTPOS), hl
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ld hl, COMPBUF
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ld (CMPDST), hl
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forthInterpret:
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call readword
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jr nz, .execute
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call find
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jr nz, .maybeNum
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ex de, hl
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call HLisIMMED
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jr z, .immed
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ex de, hl
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call .writeDE
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jr forthInterpret
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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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pop hl ; <-- lvl 1
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jr nz, .undef
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; a valid number in DE!
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ex de, hl
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ld de, NUMBER
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call .writeDE
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ex de, hl ; number in DE
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call .writeDE
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jr forthInterpret
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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 readLIT, and if it doesn't, the routine will be
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; called, triggering an abort.
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ld de, LIT
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call .writeDE
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ld de, (CMPDST)
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call strcpyM
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ld (CMPDST), de
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jr forthInterpret
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.immed:
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push hl ; --> lvl 1
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ld hl, .retRef
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call pushRS
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pop iy ; <-- lvl 1
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jp executeCodeLink
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.execute:
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ld de, QUIT
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call .writeDE
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ld iy, COMPBUF
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jp compiledWord
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.writeDE:
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push hl
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ld hl, (CMPDST)
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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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ld (CMPDST), hl
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pop hl
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ret
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.retRef:
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.dw $+2
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.dw forthInterpret
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msgOk:
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.db " ok", 0
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@ -25,6 +25,17 @@ popRS:
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dec ix
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ret
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; Skip the next two bytes in RS' TOS
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skipRS:
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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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inc hl \ inc hl
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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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; Verifies that SP is within bounds. If it's not, call ABORT
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chkPS:
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ld hl, (INITIAL_SP)
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@ -257,42 +257,6 @@ wrCompHL:
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inc iy
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ret
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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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compile:
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call find
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jr nz, .maybeNum
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ex de, hl
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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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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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.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 readLIT, 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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entryhead:
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@ -315,10 +279,8 @@ entryhead:
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xor a ; set Z
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ret
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; Sets Z if wordref at (HL) is of the IMMEDIATE type
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HLPointsIMMED:
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push hl
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call intoHL
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; Sets Z if wordref at HL is of the IMMEDIATE type
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HLisIMMED:
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dec hl
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dec hl
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dec hl
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@ -329,6 +291,13 @@ HLPointsIMMED:
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inc hl
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inc hl
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inc hl
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ret
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; Sets Z if wordref at (HL) is of the IMMEDIATE type
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HLPointsIMMED:
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push hl
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call intoHL
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call HLisIMMED
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pop hl
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ret
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@ -343,3 +312,10 @@ flagsToBC:
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dec bc
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ret
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; Write DE in (HL), advancing HL by 2.
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DEinHL:
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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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ret
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