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forth: add words "(fbr)", "(fbr?)", "'", "[']"
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Virgil Dupras
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@ -11,7 +11,7 @@
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; "jp exit".
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;
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; That's for "regular" words (words that are part of the dict chain). There are
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; also "special words", for example NUMBER, LIT, BRANCH, that have a slightly
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; also "special words", for example NUMBER, LIT, FBR, that have a slightly
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; different structure. They're also a pointer to an executable, but as for the
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; other fields, the only one they have is the "flags" field.
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@ -56,42 +56,6 @@ doesWord:
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push hl \ pop iy
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jr compiledWord
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; This word is followed by 1b *relative* offset (to the cell's addr) to where to
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; branch to. For example, The branching cell of "IF THEN" would contain 3. Add
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; this value to RS.
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branchWord:
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push de
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ld l, (ix)
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ld h, (ix+1)
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ld a, (hl)
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call addHL
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ld (ix), l
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ld (ix+1), h
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pop de
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jp exit
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.db 0b10 ; Flags
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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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jr z, branchWord
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; skip next byte in RS
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ld l, (ix)
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ld h, (ix+1)
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inc hl
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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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.db 0b10 ; Flags
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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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@ -338,10 +302,53 @@ LITERAL:
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ld (HERE), hl
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jp exit
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.db "'"
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.fill 6
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.dw LITERAL
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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 find
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jr nz, .notfound
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push de
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jp exit
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.notfound:
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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 "word not found", 0
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.db "[']"
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.fill 4
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.dw APOS
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.db 0b01 ; IMMEDIATE
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APOSI:
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.dw nativeWord
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call readword
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call find
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jr nz, .notfound
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ld hl, (HERE)
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push de ; --> lvl 1
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ld de, NUMBER
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call DEinHL
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pop de ; <-- lvl 1
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call DEinHL
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ld (HERE), hl
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jp exit
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.notfound:
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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 "word not found", 0
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; ( -- c )
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.db "KEY"
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.fill 4
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.dw LITERAL
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.dw APOSI
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.db 0
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KEY:
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.dw nativeWord
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@ -630,9 +637,49 @@ CMP:
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push bc
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jp exit
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; This word's atom is followed by 1b *relative* offset (to the cell's addr) to
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; where to branch to. For example, The branching cell of "IF THEN" would
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; contain 3. Add this value to RS.
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.db "(fbr)"
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.fill 2
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.dw CMP
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.db 0
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FBR:
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.dw nativeWord
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push de
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ld l, (ix)
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ld h, (ix+1)
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ld a, (hl)
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call addHL
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ld (ix), l
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ld (ix+1), h
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pop de
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jp exit
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; Conditional branch, only branch if TOS is zero
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.db "(fbr?)"
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.fill 1
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.dw FBR
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.db 0
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FBRC:
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.dw nativeWord
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pop hl
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ld a, h
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or l
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jr z, FBR+2
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; skip next byte in RS
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ld l, (ix)
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ld h, (ix+1)
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inc hl
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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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; : IF ' (fbr?) , HERE @ 0 C, ; IMMEDIATE
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.db "IF"
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.fill 5
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.dw CMP
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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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@ -640,7 +687,7 @@ IF:
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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, CBRANCH
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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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@ -666,7 +713,7 @@ ELSE:
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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, BRANCH
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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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@ -1,6 +1,7 @@
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Stack notation: "<stack before> -- <stack after>". Rightmost is top of stack
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(TOS). For example, in "a b -- c d", b is TOS before, d is TOS after. "R:" means
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that the Return Stack is modified.
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that the Return Stack is modified. "I:" prefix means "IMMEDIATE", that is, that
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this stack transformation is made at compile time.
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DOES>: Used inside a colon definition that itself uses CREATE, DOES> transforms
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that newly created word into a "does cell", that is, a regular cell ( when
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@ -25,29 +26,39 @@ Atom: A word of the type compiledWord contains, in its PF, a list of what we
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call "atoms". Those atoms are most of the time word references, but they can
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also be references to NUMBER and LIT.
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Words between "()" are "support words" that aren't really meant to be used
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directly, but as part of another word.
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"*I*" in description indicates an IMMEDIATE word.
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*** Defining words ***
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: x ... -- Define a new word
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; R:I -- Exit a colon definition
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, n -- Write n in HERE and advance it.
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' x -- a Push addr of word x to a.
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['] x -- *I* Like "'", but spits the addr as a number literal.
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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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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 -- Inserts number from TOS as a literal
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LITERAL 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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ELSE -- Branch to THEN
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(fbr?) f -- Conditionally branches forward by the number
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specified in its atom's cell.
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(fbr) -- Branches forward by the number specified in its
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atom's cell.
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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 n -- Branch to ELSE or THEN if n is zero
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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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RECURSE R:I -- R:I-2 Run the current word again.
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THEN -- Does nothing. Serves as a branching merker for IF
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and ELSE.
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THEN I:a -- *I* Set branching cell at a.
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*** Stack ***
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DUP a -- a a
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@ -69,12 +69,12 @@ HLPointsLIT:
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pop de
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ret
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HLPointsBRANCH:
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HLPointsBR:
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push de
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ld de, BRANCH
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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, CBRANCH
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ld de, FBRC
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call HLPointsDE
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.end:
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pop de
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@ -93,7 +93,7 @@ HLPointsEXIT:
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compSkip:
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call HLPointsNUMBER
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jr z, .isNum
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call HLPointsBRANCH
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call HLPointsBR
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jr z, .isBranch
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call HLPointsLIT
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jr nz, .isWord
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@ -171,7 +171,7 @@ readLIT:
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.notLIT:
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; Alright, not a literal, but is it a word?
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call HLPointsUNWORD
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jr nz, .notWord
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jr z, .notWord
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; Not a number, then it's a word. Copy word to pad and point to it.
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push hl ; --> lvl 1. we need it to set DE later
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call intoHL
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