forth: improve input flow

Readline, instead of being triggered by the end of execution of the last
compiled line is now triggered "just in time", by "WORD".

This allows IMMEDIATE words reading input buffer to span multiple lines
( comments for example, but colon definitions will soon follow ).

apps/forth/core.fth

@@ -7,18 +7,18 @@
 : NOT 1 SWAP SKIP? EXIT 0 * ;
 : RECURSE R> R> 2 - >R >R EXIT ;
 : ( LIT@ ) WORD SCMP NOT SKIP? RECURSE ; IMMEDIATE
-( Hello, hello, krkrkrkr... do you hear me? )
-( Ah, voice at last! Some lines above need comments )
-( BTW: Forth lines limited to 64 cols because of default )
-( input buffer size in Collapse OS )
-( NOT: a bit convulted because we don't have IF yet )
-( RECURSE: RS TOS is for RECURSE itself, then we have to dig )
-( one more level to get to RECURSE's parent's caller. )
-( IF true, skip following (fbr). Also, push br cell ref H, )
-( to PS )
+( Hello, hello, krkrkrkr... do you hear me?
+  Ah, voice at last! Some lines above need comments
+  BTW: Forth lines limited to 64 cols because of default
+  input buffer size in Collapse OS
+  NOT: a bit convulted because we don't have IF yet
+  RECURSE: RS TOS is for RECURSE itself, then we have to dig
+  one more level to get to RECURSE's parent's caller.
+  IF true, skip following (fbr). Also, push br cell ref H,
+  to PS )
 : IF ['] SKIP? , ['] (fbr) , H 1 ALLOT ; IMMEDIATE
-( Subtract TOS from H to get offset to write to IF or ELSE's )
-( br cell )
+( Subtract TOS from H to get offset to write to IF or ELSE's
+  br cell )
 : THEN DUP H -^ SWAP C! ; IMMEDIATE
 ( write (fbr) addr, allot, then same as THEN )
 : ELSE ['] (fbr) , 1 ALLOT DUP H -^ SWAP C! H 1 - ; IMMEDIATE

apps/forth/dict.asm

@@ -468,10 +468,18 @@ CURRENT_:
 	.dw sysvarWord
 	.dw CURRENT
 
+	.db	"IN>"
+	.fill	4
+	.dw	CURRENT_
+	.db	0
+INP:
+	.dw	sysvarWord
+	.dw	INPUTPOS
+
 ; ( n -- )
 	.db "."
 	.fill 6
-	.dw CURRENT_
+	.dw INP
 	.db 0
 DOT:
 	.dw nativeWord

apps/forth/dictionary.txt

@@ -112,10 +112,21 @@ LIT@ x      -- a            Read following LIT and push its addr to a
 SCMP        a1 a2 -- n      Compare strings a1 and a2. See CMP
 
 *** I/O ***
+
+A little word about inputs. There are two kind of inputs: direct and buffered.
+As a general rule, we read line in a buffer, then feed words in it to the
+interpreter. That's what "WORD" does. If it's at the End Of Line, it blocks and
+wait until another line is entered.
+
+KEY input, however, is direct. Regardless of the input buffer's state, KEY will
+return the next typed key.
+
 .           n --            Print n in its decimal form
-EMIT        c --            Spit char c to stdout
-KEY         -- c            Get char c from stdin
+EMIT        c --            Spit char c to output stream
+IN>         -- a            Address of variable containing current pos in input
+                            buffer.
+KEY         -- c            Get char c from direct input
 PC!         c a --          Spit c to port a
 PC@         a -- c          Fetch c from port a
-WORD        -- a            Read one word from stdin and push its addr
+WORD        -- a            Read one word from buffered input and push its addr
 

apps/forth/main.asm

@@ -102,13 +102,15 @@ forthMain:
 	ld	(CURRENT), hl
 	ld	hl, HERE_INITIAL
 	ld	(HERE), hl
+	; Set (INPUTPOS) to somewhere where there's a NULL so we consider
+	; ourselves EOL.
+	ld	(INPUTPOS), hl
+	xor	a
+	ld	(hl), a
 forthRdLine:
 	ld	hl, msgOk
 	call	printstr
 forthRdLineNoOk:
-	call	printcrlf
-	call	stdioReadLine
-	ld	(INPUTPOS), hl
 	; Setup return stack. After INTERPRET, we run forthExecLine
 	ld	ix, RS_ADDR
 	; We're about to compile the line and possibly execute IMMEDIATE words.
@@ -146,24 +148,18 @@ forthExecLine:
 
 ; (we don't have RECURSE here. Calling interpret makes us needlessly use our
 ; RS stack, but it can take it, can't it? )
-; WORD DUP C@ (to check if null) SKIP? (skip if not null) EXIT COMPILE INTERPRET
+; WORD COMPILE IN> @ C@ (to check if null) SKIP? (skip if not null) EXIT INTERPRET
 	.db	0b10		; UNWORD
 INTERPRET:
 	.dw	compiledWord
 	.dw	WORD
-	.dw	DUP
+	.dw	COMPILE
+	.dw	INP
+	.dw	FETCH
 	.dw	CFETCH
 	.dw	CSKIP
-	.dw	.stop
-	.dw	COMPILE
-	.dw	INTERPRET
 	.dw	EXIT
-
-.stop:
-	.dw	compiledWord
-	.dw	DROP
-	.dw	R2P
-	.dw	DROP
+	.dw	INTERPRET
 	.dw	EXIT
 
 msgOk:

apps/forth/util.asm

@@ -7,7 +7,8 @@ pad:
 ; Read word from (INPUTPOS) and return, in HL, a null-terminated word.
 ; Advance (INPUTPOS) to the character following the whitespace ending the
 ; word.
-; Z set of word was read, unset if end of line.
+; When we're at EOL, we call fetchline directly, so this call always returns
+; a word.
 readword:
 	ld	hl, (INPUTPOS)
 	; skip leading whitespace
@@ -16,6 +17,7 @@ readword:
 	inc	hl
 	ld	a, (hl)
 	or	a
+	; When at EOL, fetch a new line directly
 	jr	z, .empty
 	cp	' '+1
 	jr	c, .loop1
@@ -39,9 +41,8 @@ readword:
 	pop	hl		; <-- lvl 1. our result
 	ret	; Z set from XOR A
 .empty:
-	ld	(hl), a
-	inc	a	; unset Z
-	ret
+	call	fetchline
+	jr	readword
 
 ; Sets Z if (HL) == E and (HL+1) == D
 HLPointsDE:
@@ -336,3 +337,10 @@ DEinHL:
 	ld	(hl), d
 	inc	hl
 	ret
+
+fetchline:
+	call	printcrlf
+	call	stdioReadLine
+	ld	(INPUTPOS), hl
+	ret
+