diff --git a/apps/basic/main.asm b/apps/basic/main.asm index 9fc3785..4a81e71 100644 --- a/apps/basic/main.asm +++ b/apps/basic/main.asm @@ -4,8 +4,11 @@ ; Value of `SP` when basic was first invoked. This is where SP is going back to ; on restarts. .equ BAS_INITSP BAS_RAMSTART -; **Pointer** to current line number -.equ BAS_PCURLN @+2 +; Pointer to next line to run. If nonzero, it means that the next line is +; the first of the list. This is used by GOTO to indicate where to jump next. +; Important note: this is **not** a line number, it's a pointer to a line index +; in buffer. If it's not zero, its a valid pointer. +.equ BAS_PNEXTLN @+2 .equ BAS_SCRATCHPAD @+2 .equ BAS_RAMEND @+BAS_SCRATCHPAD_SIZE @@ -18,12 +21,12 @@ basStart: ld hl, .welcome call printstr call printcrlf - ld hl, .welcome+2 ; points to a zero word - ld (BAS_PCURLN), hl + ld hl, 0 ; points to a zero word + ld (BAS_PNEXTLN), hl jr basLoop .welcome: - .db "OK", 0, 0 + .db "OK", 0 basLoop: ld hl, .sPrompt @@ -145,6 +148,8 @@ basLIST: basRUN: + call .maybeGOTO + jr nz, .loop ; IX already set call bufFirst ret nz .loop: @@ -154,6 +159,8 @@ basRUN: call basCallCmd pop ix ; <-- lvl 1 jp nz, .err + call .maybeGOTO + jr nz, .loop ; IX already set call bufNext jr z, .loop cp a ; ensure Z @@ -169,7 +176,19 @@ basRUN: call stdioPutC jp unsetZ -.runline: +; This returns the opposite Z result as the one we usually see: Z is set if +; we **don't** goto, unset if we do. If we do, IX is properly set. +.maybeGOTO: + ld de, (BAS_PNEXTLN) + ld a, d + or e + ret z + ; we goto + push de \ pop ix + ; we need to reset our goto marker + ld de, 0 + ld (BAS_PNEXTLN), de + ret basPRINT: call parseExpr @@ -180,6 +199,22 @@ basPRINT: cp a ; ensure Z jp basPrintLn +basGOTO: + call parseExpr + ret nz + push ix \ pop de + call bufFind + jr nz, .notFound + push ix \ pop de + ; Z already set + jr .end +.notFound: + ld de, 0 + ; Z already unset +.end: + ld (BAS_PNEXTLN), de + ret + ; direct only basCmds1: .dw basBYE @@ -192,4 +227,6 @@ basCmds1: basCmds2: .dw basPRINT .db "print", 0 + .dw basGOTO + .db "goto", 0, 0 .db 0xff, 0xff, 0xff ; end of table