Make forth source compatible with both C64 and 128

immedif.fs contains implementations of immediate `[IF]` `[ELSE]` and
`[THEN]` words that can be used for conditional compilation.

This allows us to handle differences between C64 and C128 machines at
compile time instead of runtime.

Makefile

@@ -8,7 +8,7 @@ SRC_DIR = forth_src
 SRC_NAMES = base debug v asm gfx gfxdemo rnd sin ls turtle fractals \
     sprite doloop sys labels mml mmldemo sid spritedemo test testcore \
     testcoreplus tester format require compat timer float viceutil turnkey \
-    wordlist c128
+    wordlist c128 immedif
 SRCS = $(addprefix $(SRC_DIR)/,$(addsuffix .fs,$(SRC_NAMES)))
 
 EMPTY_FILE = _empty.txt

forth_src/base.fs

@@ -211,6 +211,7 @@ does> dup @ to here
 marker ---modules---
 
 .( wordlist..) include wordlist
+.( immedif..) include immedif
 .( labels..) include labels
 .( doloop..) include doloop
 .( sys..) include sys

forth_src/debug.fs

@@ -96,9 +96,11 @@ last-dump ! base ! ;
 : n last-dump @ dump ;
 hide last-dump
 
-: more 
-$eb c@ $18 = if
-0 $f4 c! \ exit quoted state
+: more
+\ current cursor y pos
+[ native-c128? ]
+[if] $eb [else] $d6 [then] 
+c@ $18 = if 
 $12 emit ." more" $92 emit 
 key drop page then ;
 

forth_src/immedif.fs

@@ -0,0 +1,38 @@
+\ Immediate versions of if/else/then to
+\ allow conditional compilation.
+\ Supports nesting.
+
+header [if] ( -- ) immediate
+
+: [then] ( -- ) ; immediate 
+
+: [else] ( -- )
+\ consume and discard following words
+\ until a matching [else] or [then] is
+\ encountered
+1 begin
+    begin parse-name dup while
+        find-name case
+        [ parse-name [if] find-name ] 
+        literal of 
+            1+
+        endof
+        [ latest ] literal of
+            1-
+            dup if 1+ then
+        endof
+        [ parse-name [then] find-name ] 
+        literal of
+            1- 
+        endof
+        endcase
+        ?dup 0= if exit then
+    repeat
+    source nip drop 0= if refill then
+    source nip drop 0= until
+drop
+; immediate
+
+define [if] ( flag -- )
+0= if postpone [else] then
+; \ immediate flag set in header

forth_src/v.fs

@@ -74,15 +74,20 @@ $400 + ( addr ) ;
 
 : sol 0 curx ! ;
 
+native-c128? [if]
+: rom-kernal ;
+: ram-kernal ;
+[else]
 \ ram + io + kernal rom
 \ skip on c128
 code rom-kernal
-\ $36 lda,# 1 sta, 
+$36 lda,# 1 sta,
 ;code
 \ ram + io + ram
 code ram-kernal
-\ $35 lda,# 1 sta, 
+$35 lda,# 1 sta,
 ;code
+[then]
 
 : reset-buffer
 0 bufstart 1- c!
@@ -195,17 +200,20 @@ or advance-cur or until ;
 begin advance-cur editpos 1+ dup
 eof= swap c@ space= or or until ;
 
-\ : setcur ( x y -- )
-\ xr ! yr ! $fff0 [ clc, ] sys ;
-
+native-c128? [if]
 \ SYS doesn't work yet on the 128
 \ this code works on both 64 and 128
 code setcur ( x y -- )
 lsb lda,x inx, lsb ldy,x inx,
 w stx, tax,
-clc, $fff0 jsr, \ PLOT, 
+clc, $fff0 jsr, \ PLOT 
 w ldx,
 ;code
+[else]
+: setcur ( x y -- )
+xr ! yr ! $fff0 [ clc, ] sys ;
+[then]
+
 
 : refresh-line
 cury @ $28 * $400 + $28 bl fill
@@ -630,16 +638,17 @@ curlinestart @ bufstart eof @ within
 0= abort" cl" again ;
 
 define v
-\ modifies kernal to change kbd prefs
-\ skip on 128
-( 
-  ram-kernal $eaea @ $8ca <> if
+[ native-c128? ] [if]
+\ C128: 
+[else]
+\ C64: modify kernal to change kbd prefs
+ram-kernal $eaea @ $8ca <> if
 rom-kernal
 $e000 dup $2000 move \ rom => ram
 $f $eaea c! \ repeat delay
 4 $eb1d c! \ repeat speed
 then
-)
+[then]
 
 0 to insert
 $80 $28a c! \ key repeat on