From 764b2222c7bce6a109b6dc496f196bcd55b61225 Mon Sep 17 00:00:00 2001
From: Virgil Dupras <hsoft@hardcoded.net>
Date: Sat, 14 Mar 2020 09:23:58 -0400
Subject: [PATCH] forth: replace (fbr?) by SKIP?

This will allow us to support backward branching with just one new (bbr) word.
Also, this allow us to have "(" word sooned in core.fth and thus allow for
earlier commenting.
---
 apps/forth/core.fth       | 22 +++++++++++++---------
 apps/forth/dict.asm       | 36 +++++++++++++++++-------------------
 apps/forth/dictionary.txt |  5 +++--
 apps/forth/util.asm       |  4 ----
 4 files changed, 33 insertions(+), 34 deletions(-)

diff --git a/apps/forth/core.fth b/apps/forth/core.fth
index 6aab627..b01ddc7 100644
--- a/apps/forth/core.fth
+++ b/apps/forth/core.fth
@@ -4,20 +4,24 @@
 : ALLOT HERE +! ;
 : , H ! 2 ALLOT ;
 : C, H C! 1 ALLOT ;
-: IF ['] (fbr?) , H 1 ALLOT ; IMMEDIATE
-: THEN DUP H -^ SWAP C! ; IMMEDIATE
-: ELSE ['] (fbr) , 1 ALLOT DUP H -^ SWAP C! H 1 - ; IMMEDIATE
+: NOT 1 SWAP SKIP? EXIT 0 * ;
 : RECURSE R> R> 2 - >R >R EXIT ;
-: ( LIT@ ) WORD SCMP IF RECURSE THEN ; IMMEDIATE
+: ( LIT@ ) WORD SCMP NOT SKIP? RECURSE ; IMMEDIATE
 ( Hello, hello, krkrkrkr... do you hear me? )
 ( Ah, voice at last! Some lines above need comments )
-( IF: write (fbr?) addr, push HERE, create cell )
-( THEN: Subtract TOS from H to get offset to write to cell )
-( in that same TOS's addr )
-( ELSE: write (fbr) addr, allot, then same as THEN )
+( 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. )
-: NOT IF 0 ELSE 1 THEN ;
+( 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 )
+: 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
 : ? @ . ;
 : VARIABLE CREATE 2 ALLOT ;
 : CONSTANT CREATE H ! DOES> @ ;
diff --git a/apps/forth/dict.asm b/apps/forth/dict.asm
index 6667760..9d66136 100644
--- a/apps/forth/dict.asm
+++ b/apps/forth/dict.asm
@@ -711,12 +711,27 @@ CMP:
 	push	bc
 	jp	next
 
+	.db	"SKIP?"
+	.fill	2
+	.dw	CMP
+	.db	0
+CSKIP:
+	.dw	nativeWord
+	pop	hl
+	ld	a, h
+	or	l
+	jp	z, next		; False, do nothing.
+	ld	hl, (IP)
+	call	compSkip
+	ld	(IP), hl
+	jp	next
+
 ; This word's atom is followed by 1b *relative* offset (to the cell's addr) to
 ; where to branch to. For example, The branching cell of "IF THEN" would
 ; contain 3. Add this value to RS.
 	.db	"(fbr)"
 	.fill	2
-	.dw	CMP
+	.dw	CSKIP
 	.db	0
 FBR:
 	.dw	nativeWord
@@ -728,23 +743,6 @@ FBR:
 	pop	de
 	jp	next
 
-; Conditional branch, only branch if TOS is zero
-	.db	"(fbr?)"
-	.fill	1
-	.dw	FBR
-	.db	0
-FBRC:
-	.dw	nativeWord
-	pop	hl
-	ld	a, h
-	or	l
-	jr	z, FBR+2
-	; skip next byte in RS
-	ld	hl, (IP)
-	inc	hl
-	ld	(IP), hl
-	jp	next
-
 LATEST:
-	.dw FBRC
+	.dw FBR
 
diff --git a/apps/forth/dictionary.txt b/apps/forth/dictionary.txt
index 230e455..ecf236e 100644
--- a/apps/forth/dictionary.txt
+++ b/apps/forth/dictionary.txt
@@ -49,8 +49,6 @@ LITERAL     n --            *I* Inserts number from TOS as a literal
 VARIABLE c  --              Creates cell x with 2 bytes allocation.
 
 *** Flow ***
-(fbr?)      f --            Conditionally branches forward by the number
-                            specified in its atom's cell.
 (fbr)       --              Branches forward by the number specified in its
                             atom's cell.
 ELSE        I:a --          *I* Compiles a (fbr) and set branching cell at a.
@@ -60,6 +58,9 @@ INTERPRET   --              Get a line from stdin, compile it in tmp memory,
                             then execute the compiled contents.
 QUIT        R:drop --       Return to interpreter promp immediately
 RECURSE     R:I -- R:I-2    Run the current word again.
+SKIP?       f --            If f is true, skip the execution of the next atom.
+                            Use this right before ";" and you're gonna have a
+                            bad time.
 THEN        I:a --          *I* Set branching cell at a.
 
 *** Parameter Stack ***
diff --git a/apps/forth/util.asm b/apps/forth/util.asm
index 4dec153..b2b1a7d 100644
--- a/apps/forth/util.asm
+++ b/apps/forth/util.asm
@@ -73,10 +73,6 @@ HLPointsBR:
 	push	de
 	ld	de, FBR
 	call	HLPointsDE
-	jr	z, .end
-	ld	de, FBRC
-	call	HLPointsDE
-.end:
 	pop	de
 	ret