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forth: remove CMPDST
We now always do ","-style writes in (HERE), even in IMMEDIATE mode. Simplifies things and paves the way for compiling words in Forth.
This commit is contained in:
Virgil Dupras
parent
ff281f69a8
commit
3819dbc083
@ -332,12 +332,12 @@ IMMEDIATE:
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.db 1 ; IMMEDIATE
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LITERAL:
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.dw nativeWord
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ld hl, (CMPDST)
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ld hl, (HERE)
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ld de, NUMBER
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call DEinHL
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pop de ; number from stack
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call DEinHL
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ld (CMPDST), hl
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ld (HERE), hl
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jp exit
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; ( -- c )
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@ -641,12 +641,12 @@ IF:
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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, (CMPDST)
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ld hl, (HERE)
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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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inc hl ; empty 1b cell
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ld (CMPDST), hl
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ld (HERE), hl
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jp exit
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.db "ELSE"
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@ -657,7 +657,7 @@ 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, (CMPDST)
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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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@ -667,12 +667,12 @@ ELSE:
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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 hl, (HERE)
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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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inc hl ; empty 1b cell
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ld (CMPDST), hl
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ld (HERE), hl
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jp exit
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.db "THEN"
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@ -683,7 +683,7 @@ THEN:
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.dw nativeWord
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; See comments in IF and ELSE
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pop de ; cell's address
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ld hl, (CMPDST)
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ld hl, (HERE)
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; There is nothing to skip because THEN leaves nothing.
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or a ; clear carry
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sbc hl, de ; HL now has relative offset
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@ -21,9 +21,6 @@
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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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@ -38,19 +35,29 @@
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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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; 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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; 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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; 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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; *** Code ***
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forthMain:
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@ -78,8 +85,12 @@ forthRdLine:
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call stdioReadLine
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ld ix, RS_ADDR-2 ; -2 because we inc-before-push
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ld (INPUTPOS), hl
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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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push hl ; Saving HERE
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ld hl, COMPBUF
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ld (CMPDST), hl
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ld (HERE), hl
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forthInterpret:
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call readword
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jr nz, .execute
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@ -111,9 +122,9 @@ forthInterpret:
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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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ld de, (HERE)
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call strcpyM
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ld (CMPDST), de
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ld (HERE), de
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jr forthInterpret
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.immed:
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push hl ; --> lvl 1
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@ -124,16 +135,19 @@ forthInterpret:
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.execute:
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ld de, QUIT
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call .writeDE
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; Compilation done, let's restore (HERE) and execute!
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pop hl ; Restore old (HERE)
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ld (HERE), hl
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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, (HERE)
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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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ld (HERE), hl
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pop hl
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ret
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