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forth: Simplify execution model
Change the mainloop so that words are executed immediately after they're read. This greatly simplifies execution model and allow the "DEFINE" word to become an IMMEDIATE and stop its "copy from compiled words" scheme. The downside to this is that flow control words no longer work when being used directly in the input buffer. They only work as part of a definition. It also broke "RECURSE", but I've replaced it with "BEGIN" and "AGAIN". Another effect of this change is that definitions can now span multiple lines. All in all, it feels good to get rid of that COMPBUF...
This commit is contained in:
Virgil Dupras
parent
7befe56597
commit
80ab395823
@ -4,16 +4,15 @@
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: ALLOT HERE +! ;
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: , H ! 2 ALLOT ;
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: C, H C! 1 ALLOT ;
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: BEGIN H ; IMMEDIATE
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: AGAIN ['] (bbr) , H -^ C, ; IMMEDIATE
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: NOT 1 SWAP SKIP? EXIT 0 * ;
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: RECURSE R> R> 2 - >R >R EXIT ;
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: ( LIT@ ) WORD SCMP NOT SKIP? RECURSE ; IMMEDIATE
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: ( BEGIN LITS ) WORD SCMP NOT SKIP? AGAIN ; 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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BTW: Forth lines limited to 64 cols because of default
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input buffer size in Collapse OS
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NOT: a bit convulted because we don't have IF yet
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RECURSE: RS TOS is for RECURSE itself, then we have to dig
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one more level to get to RECURSE's parent's caller.
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IF true, skip following (fbr). Also, push br cell ref H,
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to PS )
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: IF ['] SKIP? , ['] (fbr) , H 1 ALLOT ; IMMEDIATE
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@ -97,17 +97,14 @@ NUMBER:
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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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; null-terminated string. When called, puts the string's address on PS
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litWord:
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ld hl, (IP)
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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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push hl
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call strskip
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inc hl ; after null termination
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ld (IP), hl
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jp next
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.db 0b10 ; Flags
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LIT:
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@ -142,11 +139,24 @@ quit:
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ABORT:
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.dw nativeWord
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abort:
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; flush rest of input
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ld hl, (INPUTPOS)
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xor a
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ld (hl), a
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; Reinitialize PS (RS is reinitialized in forthInterpret)
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ld sp, (INITIAL_SP)
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jp forthRdLineNoOk
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ABORTREF:
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.dw ABORT
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; prints msg in (HL) then aborts
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abortMsg:
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call printstr
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jr abort
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abortUnknownWord:
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ld hl, .msg
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jr abortMsg
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.msg:
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.db "unknown word", 0
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.db "BYE"
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.fill 4
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@ -220,7 +230,7 @@ EXECUTE:
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.db 1 ; IMMEDIATE
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COMPILE:
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.dw nativeWord
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pop hl ; word addr
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call readword
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call find
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jr nz, .maybeNum
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ex de, hl
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@ -242,29 +252,11 @@ COMPILE:
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call .writeDE
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jp next
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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, (HERE)
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call strcpyM
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ld (HERE), de
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jp next
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call printstr
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jp abortUnknownWord
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.immed:
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; For this IMMEDIATE word to be compatible with regular execution model,
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; it needs to be compiled as an atom somewhere in memory.
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; For example, RECURSE backtracks in RS and steps back 2 bytes. This
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; can only work with our compiled atom being next to an EXIT atom.
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ex de, hl ; atom to write in DE
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ld hl, (OLDHERE)
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push hl \ pop iy
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call DEinHL
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ld de, EXIT
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call DEinHL
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jp compiledWord
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push hl
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jp EXECUTE+2
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.writeDE:
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push hl
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ld hl, (HERE)
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@ -274,56 +266,49 @@ COMPILE:
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ret
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.db ";"
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.db ":"
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.fill 6
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.dw COMPILE
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.db 0
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ENDDEF:
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.dw nativeWord
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jp EXIT+2
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.db ":"
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.fill 6
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.dw ENDDEF
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.db 0
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.db 1 ; IMMEDIATE
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DEFINE:
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.dw nativeWord
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call entryhead
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ld de, compiledWord
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call DEinHL
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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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ex de, hl ; DE is our dest
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ld (HERE), de ; update HERE
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ld hl, (IP)
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ld (HERE), hl
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.loop:
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push de ; --> lvl 1
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ld de, ENDDEF
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call HLPointsDE
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pop de ; <-- lvl 1
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jr z, .loopend
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call compSkip
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jr .loop
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.loopend:
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; skip EXIT
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inc hl \ inc hl
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; We have out end offset. Let's get our offset
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ld de, (IP)
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or a ; clear carry
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sbc hl, de
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; HL is our copy count.
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ld b, h
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ld c, l
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; did we reach ";"?
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ld hl, (INPUTPOS)
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ld a, (hl)
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cp ';'
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jr nz, .compile
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inc hl
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ld a, (hl)
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cp ' '+1
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jr c, .loopend ; whitespace, we have semicol. end
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.compile:
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ld hl, (IP)
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ld de, (HERE) ; recall dest
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; copy!
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ldir
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call pushRS
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ld hl, .retRef
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ld (IP), hl
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ld (HERE), de
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ld hl, COMPILE
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push hl
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jp EXECUTE+2
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.loopend:
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; Advance (INPUTPOS) to after semicol. HL is already there.
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ld (INPUTPOS), hl
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; write EXIT and return
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ld hl, (HERE)
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ld de, EXIT
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call DEinHL
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ld (HERE), hl
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jp next
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.retRef:
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.dw $+2
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.dw $+2
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call popRS
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ld (IP), hl
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jr .loop
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.db "DOES>"
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@ -359,10 +344,11 @@ IMMEDIATE:
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jp next
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; ( n -- )
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.db "LITERAL"
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.dw IMMEDIATE
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.db 1 ; IMMEDIATE
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LITERAL:
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.db "LITN"
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.fill 3
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.dw IMMEDIATE
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.db 1 ; IMMEDIATE
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LITN:
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.dw nativeWord
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ld hl, (HERE)
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ld de, NUMBER
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@ -372,14 +358,28 @@ LITERAL:
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ld (HERE), hl
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jp next
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.db "LITS"
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.fill 3
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.dw LITN
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.db 1 ; IMMEDIATE
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LITS:
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.dw nativeWord
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ld hl, (HERE)
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ld de, LIT
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call DEinHL
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ex de, hl ; (HERE) in DE
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call readword
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call strcpyM
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ld (HERE), de
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jp next
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.db "'"
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.fill 6
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.dw LITERAL
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.dw LITS
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.db 0
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APOS:
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.dw nativeWord
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call readLITBOS
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call readword
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call find
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jr nz, .notfound
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push de
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@ -542,20 +542,10 @@ CFETCH:
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push hl
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jp next
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.db "LIT@"
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.fill 3
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.dw CFETCH
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.db 0
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LITFETCH:
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.dw nativeWord
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call readLITTOS
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push hl
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jp next
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; ( a -- )
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.db "DROP"
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.fill 3
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.dw LITFETCH
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.dw CFETCH
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.db 0
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DROP:
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.dw nativeWord
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@ -818,6 +808,19 @@ FBR:
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pop de
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jp next
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LATEST:
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.dw FBR
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.db "(bbr)"
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.fill 2
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.dw FBR
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.db 0
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BBR:
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.dw nativeWord
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ld hl, (IP)
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ld d, 0
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ld e, (hl)
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or a ; clear carry
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sbc hl, de
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ld (IP), hl
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jp next
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LATEST:
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.dw BBR
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@ -42,22 +42,30 @@ directly, but as part of another word.
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ALLOT n -- Move HERE by n bytes
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C, b -- Write byte b in HERE and advance it.
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CREATE x -- Create cell named x. Doesn't allocate a PF.
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COMPILE x -- Compile word x and write it to HERE
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CONSTANT x n -- Creates cell x that when called pushes its value
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DOES> -- See description at top of file
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IMMEDIATE -- Flag the latest defined word as immediate.
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LITERAL n -- *I* Inserts number from TOS as a literal
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LITN n -- *I* Inserts number from TOS as a literal
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VARIABLE c -- Creates cell x with 2 bytes allocation.
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*** Flow ***
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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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COMPILE a -- Compile string word at addr a and spit it to HERE.
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(bbr) -- Branches backward by the number specified in its
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atom's cell.
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AGAIN I:a -- *I* Jump backwards to preceeding BEGIN.
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BEGIN -- I:a *I* Marker for backward branching with AGAIN.
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ELSE I:a -- *I* Compiles a (fbr) and set branching cell at a.
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EXECUTE a -- Execute wordref at addr a
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IF -- I:a *I* Compiles a (fbr?) and pushes its cell's addr
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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 promp immediately
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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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@ -108,7 +116,7 @@ CMP n1 n2 -- n Compare n1 and n2 and set n to -1, 0, or 1.
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NOT f -- f Push the logical opposite of f
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*** Strings ***
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LIT@ x -- a Read following LIT and push its addr to a
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LITS x -- a Read following LIT and push its addr to a
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SCMP a1 a2 -- n Compare strings a1 and a2. See CMP
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*** I/O ***
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@ -19,18 +19,14 @@
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.equ INITIAL_SP FORTH_RAMSTART
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; wordref of the last entry of the dict.
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.equ CURRENT @+2
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; Pointer to the next free byte in dict. During compilation of input text, this
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; temporarily points to the next free byte in COMPBUF.
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; Pointer to the next free byte in dict.
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.equ HERE @+2
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; Used to hold HERE while we temporarily point it to COMPBUF
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.equ OLDHERE @+2
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; Interpreter pointer. See Execution model comment below.
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.equ IP @+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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; 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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.equ FORTH_RAMEND @+2
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; (HERE) usually starts at RAMEND, but in certain situations, such as in stage0,
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; (HERE) will begin at a strategic place.
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@ -41,30 +37,11 @@
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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. if immediate, execute atom
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; 4. goto 1 until we exhaust words
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; 5. Execute compiled atom list as if it was a regular compiledWord.
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;
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; Because the Parameter Stack uses SP, 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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;
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; HERE and IMMEDIATE: When compiling in step 2, we spit compiled atoms in
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; (HERE) to simplify "," semantic in Forth (spitting, in all cases, is done in
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; (HERE)). However, suring input line compilation, it isn't like during ":", we
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; aren't creating a new entry.
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;
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; Compiling and executing from (HERE) would be dangerous because an
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; entry-creation word, during runtime, could end up overwriting the atom list
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; we're executing. This is why we have this list in COMPBUF.
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;
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; During IMMEDIATE mode, (HERE) is temporarily set to COMPBUF, and when we're
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; done, we restore (HERE) for runtime. This way, everyone is happy.
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; 2. Can we find the word in dict?
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; 3. If yes, execute that word, goto 1
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; 4. Is it a number?
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; 5. If yes, push that number to PS, goto 1
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; 6. Error: undefined word.
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;
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; EXECUTING A WORD
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;
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@ -113,54 +90,45 @@ forthRdLine:
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forthRdLineNoOk:
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; Setup return stack. After INTERPRET, we run forthExecLine
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ld ix, RS_ADDR
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; We're about to compile the line and possibly execute IMMEDIATE words.
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; Let's save current (HERE) and temporarily set it to COMPBUF.
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ld hl, (HERE)
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ld (OLDHERE), hl
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ld hl, COMPBUF
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ld (HERE), hl
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ld hl, .retRef
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ld (IP), hl
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ld hl, INTERPRET
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ld hl, MAINLOOP
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push hl
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jp EXECUTE+2
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.retRef:
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.dw $+2
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.dw forthExecLine
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forthExecLine:
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ld de, QUIT
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ld hl, (HERE)
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call DEinHL
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ld (HERE), hl
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; Compilation done, let's restore (HERE) and execute!
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ld hl, (OLDHERE)
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ld (HERE), hl
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ld iy, COMPBUF
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; before we execute, let's play with our RS a bit: compiledWord is
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; going to push (IP) on the RS, but we don't expect our compiled words
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; to ever return: it ends with QUIT. Let's set (IP) to ABORTREF and
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; IX to RS_ADDR-2 so that compiledWord re-pushes our safety net.
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ld hl, ABORTREF
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ld (IP), hl
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ld ix, RS_ADDR-2
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jp compiledWord
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; (we don't have RECURSE here. Calling interpret makes us needlessly use our
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; RS stack, but it can take it, can't it? )
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; WORD COMPILE IN> @ C@ (to check if null) SKIP? (skip if not null) EXIT INTERPRET
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.db 0b10 ; UNWORD
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INTERPRET:
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.dw nativeWord
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pop hl ; from WORD
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ld a, (hl) ; special case: empty
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or a
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jp z, next
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call find
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jr nz, .maybeNum
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; regular word
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push de
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jp EXECUTE+2
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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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push de
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jp next
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.undef:
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call printstr
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jp abortUnknownWord
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.db 0b10 ; UNWORD
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MAINLOOP:
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.dw compiledWord
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.dw WORD
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.dw COMPILE
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.dw INTERPRET
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.dw INP
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.dw FETCH
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.dw CFETCH
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.dw CSKIP
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.dw EXIT
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.dw INTERPRET
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.dw EXIT
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.dw QUIT
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.dw MAINLOOP
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msgOk:
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.db " ok", 0
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@ -74,6 +74,10 @@ HLPointsBR:
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push de
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ld de, FBR
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call HLPointsDE
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jr z, .end
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ld de, BBR
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||||
call HLPointsDE
|
||||
.end:
|
||||
pop de
|
||||
ret
|
||||
|
||||
@ -105,121 +109,6 @@ compSkip:
|
||||
inc hl \ inc hl
|
||||
ret
|
||||
|
||||
; ***readLIT***
|
||||
; The goal of this routine is to read a string literal following the currently
|
||||
; executed words. For example, CREATE and DEFINE need this. Things are a little
|
||||
; twisted, so bear with me while I explain how it works.
|
||||
;
|
||||
; When we call this routine, everything has been compiled. We're on an atom and
|
||||
; we're executing it. Now, we're looking for a string literal or a word-with-a
|
||||
; name that follows our readLIT caller. We could think that this word is
|
||||
; right there on RS' TOS, but not always! You have to account for words wrapping
|
||||
; the caller. For example, "VARIABLE" calls "CREATE". If you call
|
||||
; "VARIABLE foo", if CREATE looks at what follows in RS' TOS, it will only find
|
||||
; the "2" in "CREATE 2 ALLOT".
|
||||
;
|
||||
; In this case, we actually need to check in RS' *bottom of stack* for our
|
||||
; answer. If that atom is a LIT, we're good. We make HL point to it and advance
|
||||
; IP to byte following null-termination.
|
||||
;
|
||||
; If it isn't, things get interesting: If it's a word reference, then it's
|
||||
; not an invalid literal. For example, one could want to redefine an existing
|
||||
; word. So in that case, we'll copy the word's name on the pad (it might not be
|
||||
; null-terminated) and set HL to point to it.
|
||||
; How do we know that our reference is a word reference (it could be, for
|
||||
; example, a NUMBER reference)? We check that its address is more than QUIT, the
|
||||
; second word in our dict. We don't accept EXIT because it's the termination
|
||||
; word. Yeah, it means that ";" can't be overridden...
|
||||
; If name can't be read, we abort
|
||||
;
|
||||
; BOS vs TOS: What we cover so far is the "CREATE" and friends cases, where we
|
||||
; want to read BOS. There are, however, cases where we want to read TOS, that is
|
||||
; that we want to read the LIT right next to our atom. Example: "(". When
|
||||
; processing comments, we are at compile time and want to read words from BOS,
|
||||
; yes), however, in "("'s definition, there's "LIT@ )", which means "fetch LIT
|
||||
; next to me and push this to stack". This LIT we want to fetch is *not* from
|
||||
; BOS, it's from TOS.
|
||||
;
|
||||
; This is why we have readLITBOS and readLITTOS. readLIT uses HL and DE and is
|
||||
; not used directly.
|
||||
|
||||
; Given a RS stack pointer HL, read LIT next to it (or abort) and set HL to
|
||||
; point to its associated string. Set DE to there the RS stack pointer should
|
||||
; point next.
|
||||
readLIT:
|
||||
call HLPointsLIT
|
||||
jr nz, .notLIT
|
||||
; RS BOS is a LIT, make HL point to string, then skip this RS compword.
|
||||
inc hl \ inc hl ; HL now points to string itself
|
||||
; HL has our its final value
|
||||
ld d, h
|
||||
ld e, l
|
||||
call strskip
|
||||
inc hl ; byte after word termination
|
||||
ex de, hl
|
||||
ret
|
||||
.notLIT:
|
||||
; Alright, not a literal, but is it a word?
|
||||
call HLPointsUNWORD
|
||||
jr z, .notWord
|
||||
; Not a number, then it's a word. Copy word to pad and point to it.
|
||||
push hl ; --> lvl 1. we need it to set DE later
|
||||
call intoHL
|
||||
or a ; clear carry
|
||||
ld de, CODELINK_OFFSET
|
||||
sbc hl, de
|
||||
; That's our return value
|
||||
push hl ; --> lvl 2
|
||||
; HL now points to word offset, let'd copy it to pad
|
||||
ex de, hl
|
||||
call pad
|
||||
ex de, hl
|
||||
ld bc, NAMELEN
|
||||
ldir
|
||||
; null-terminate
|
||||
xor a
|
||||
ld (de), a
|
||||
pop hl ; <-- lvl 2
|
||||
pop de ; <-- lvl 1
|
||||
; Advance IP by 2
|
||||
inc de \ inc de
|
||||
ret
|
||||
.notWord:
|
||||
ld hl, .msg
|
||||
call printstr
|
||||
jp abort
|
||||
.msg:
|
||||
.db "word expected", 0
|
||||
|
||||
readLITBOS:
|
||||
; Before we start: is our RS empty? If IX == RS_ADDR, it is (it only has
|
||||
; its safety net). When that happens, we actually want to run readLITTOS
|
||||
push hl
|
||||
push de
|
||||
push ix \ pop hl
|
||||
ld de, RS_ADDR
|
||||
or a ; clear carry
|
||||
sbc hl, de
|
||||
pop de
|
||||
pop hl
|
||||
jr z, readLITTOS
|
||||
push de
|
||||
; Our bottom-of-stack is RS_ADDR+2 because RS_ADDR is occupied by our
|
||||
; ABORTREF safety net.
|
||||
ld hl, (RS_ADDR+2)
|
||||
call readLIT
|
||||
ld (RS_ADDR+2), de
|
||||
pop de
|
||||
ret
|
||||
|
||||
readLITTOS:
|
||||
push de
|
||||
ld hl, (IP)
|
||||
call readLIT
|
||||
ld (IP), de
|
||||
pop de
|
||||
ret
|
||||
|
||||
; Find the entry corresponding to word where (HL) points to and sets DE to
|
||||
; point to that entry.
|
||||
; Z if found, NZ if not.
|
||||
@ -271,7 +160,7 @@ wrCompHL:
|
||||
; Spit name + prev in (HERE) and adjust (HERE) and (CURRENT)
|
||||
; HL points to new (HERE)
|
||||
entryhead:
|
||||
call readLITBOS
|
||||
call readword
|
||||
ld de, (HERE)
|
||||
call strcpy
|
||||
ex de, hl ; (HERE) now in HL
|
||||
@ -343,4 +232,3 @@ fetchline:
|
||||
call stdioReadLine
|
||||
ld (INPUTPOS), hl
|
||||
ret
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user