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https://github.com/hsoft/collapseos.git
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289037a3dd
HL, instead of being preserved, is set to the character following the last read character.
532 lines
9.5 KiB
NASM
532 lines
9.5 KiB
NASM
; *** Variables ***
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; Value of `SP` when basic was first invoked. This is where SP is going back to
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; on restarts.
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.equ BAS_INITSP BAS_RAMSTART
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; Pointer to next line to run. If nonzero, it means that the next line is
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; the first of the list. This is used by GOTO to indicate where to jump next.
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; Important note: this is **not** a line number, it's a pointer to a line index
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; in buffer. If it's not zero, its a valid pointer.
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.equ BAS_PNEXTLN @+2
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; Points to a routine to call when a command isn't found in the "core" cmd
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; table. This gives the opportunity to glue code to configure extra commands.
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.equ BAS_FINDHOOK @+2
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.equ BAS_RAMEND @+2
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; *** Code ***
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basInit:
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ld (BAS_INITSP), sp
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call varInit
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call bufInit
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xor a
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ld (BAS_PNEXTLN), a
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ld (BAS_PNEXTLN+1), a
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ld hl, unsetZ
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ld (BAS_FINDHOOK), hl
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ret
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basStart:
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ld hl, .welcome
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call printstr
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call printcrlf
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jr basLoop
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.welcome:
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.db "Collapse OS", 0
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basLoop:
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ld hl, .sPrompt
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call printstr
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call stdioReadLine
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call printcrlf
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call parseDecimalC
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jr z, .number
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ld de, basCmds1
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call basCallCmds
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jr z, basLoop
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; Error
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call basERR
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jr basLoop
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.number:
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call rdSep
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call bufAdd
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jp nz, basERR
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jr basLoop
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.sPrompt:
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.db "> ", 0
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; Tries to find command specified in (DE) (must be null-terminated) in cmd
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; table in (HL). If found, sets IX to point to the associated routine. If
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; not found, calls BAS_FINDHOOK so that we look through extra commands
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; configured by glue code.
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; Destroys HL.
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; Z is set if found, unset otherwise.
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basFindCmd:
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.loop:
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call strcmp
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call strskip
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inc hl ; point to routine
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jr z, .found ; Z from strcmp
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inc hl \ inc hl ; skip routine
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ld a, (hl)
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inc a ; was it 0xff?
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jr nz, .loop ; no
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dec a ; unset Z
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ret
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.found:
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call intoHL
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push hl \ pop ix
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ret
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; Call command in (HL) after having looked for it in cmd table in (DE).
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; If found, jump to it. If not found, try (BAS_FINDHOOK). If still not found,
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; unset Z. We expect commands to set Z on success. Therefore, when calling
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; basCallCmd results in NZ, we're not sure where the error come from, but
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; well...
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basCallCmd:
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; let's see if it's a variable assignment.
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call varTryAssign
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ret z ; Done!
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push de ; --> lvl 1.
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ld de, SCRATCHPAD
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call rdWord
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; cmdname to find in (DE)
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; How lucky, we have a legitimate use of "ex (sp), hl"! We have the
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; cmd table in the stack, which we want in HL and we have the rest of
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; the cmdline in (HL), which we want in the stack!
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ex (sp), hl
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call basFindCmd
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jr z, .skip
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; not found, try BAS_FINDHOOK
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ld ix, (BAS_FINDHOOK)
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call callIX
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.skip:
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; regardless of the result, we need to balance the stack.
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; Bring back rest of the command string from the stack
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pop hl ; <-- lvl 1
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ret nz
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; cmd found, skip whitespace and then jump!
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call rdSep
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jp (ix)
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; Call a series of ':'-separated commands in (HL) using cmd table in (DE).
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; Stop processing as soon as one command unsets Z.
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basCallCmds:
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; Commands are not guaranteed at all to preserve HL and DE, so we
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; preserve them ourselves here.
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push hl ; --> lvl 1
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push de ; --> lvl 2
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call basCallCmd
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pop de ; <-- lvl 2
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pop hl ; <-- lvl 1
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ret nz
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call toEnd
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ret z ; no more cmds
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; we met a ':', we have more cmds
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inc hl
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call basCallCmds
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; move the the end of the string so that we don't run cmds following a
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; ':' twice.
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call strskip
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ret
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basERR:
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ld hl, .sErr
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call printstr
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jp printcrlf
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.sErr:
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.db "ERR", 0
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; *** Commands ***
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; A command receives its argument through (HL), which is already placed to
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; either:
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; 1 - the end of the string if the command has no arg.
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; 2 - the beginning of the arg, with whitespace properly skipped.
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;
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; Commands are expected to set Z on success.
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basLIST:
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call bufFirst
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jr nz, .end
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.loop:
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ld e, (ix)
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ld d, (ix+1)
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ld hl, SCRATCHPAD
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call fmtDecimal
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call printstr
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ld a, ' '
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call stdioPutC
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call bufStr
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call printstr
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call printcrlf
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call bufNext
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jr z, .loop
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.end:
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cp a ; ensure Z
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ret
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basRUN:
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call .maybeGOTO
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jr nz, .loop ; IX already set
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call bufFirst
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ret nz
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.loop:
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call bufStr
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ld de, basCmds2
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push ix ; --> lvl 1
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call basCallCmds
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pop ix ; <-- lvl 1
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jp nz, .err
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call .maybeGOTO
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jr nz, .loop ; IX already set
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call bufNext
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jr z, .loop
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cp a ; ensure Z
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ret
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.err:
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; Print line number, then return NZ (which will print ERR)
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ld e, (ix)
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ld d, (ix+1)
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ld hl, SCRATCHPAD
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call fmtDecimal
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call printstr
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ld a, ' '
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call stdioPutC
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jp unsetZ
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; This returns the opposite Z result as the one we usually see: Z is set if
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; we **don't** goto, unset if we do. If we do, IX is properly set.
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.maybeGOTO:
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ld de, (BAS_PNEXTLN)
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ld a, d
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or e
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ret z
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; we goto
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push de \ pop ix
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; we need to reset our goto marker
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ld de, 0
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ld (BAS_PNEXTLN), de
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ret
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basPRINT:
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; Do we have arguments at all? if not, it's not an error, just print
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; crlf
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ld a, (hl)
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or a
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jr z, .end
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; Is our arg a string literal?
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call spitQuoted
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jr z, .chkAnother ; string printed, skip to chkAnother
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ld de, SCRATCHPAD
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call rdWord
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push hl ; --> lvl 1
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ex de, hl
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call parseExpr
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jr nz, .parseError
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ld hl, SCRATCHPAD
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call fmtDecimalS
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call printstr
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pop hl ; <-- lvl 1
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.chkAnother:
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; Do we have another arg?
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call rdSep
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jr z, .another
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; no, we can stop here
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.end:
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cp a ; ensure Z
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jp printcrlf
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.another:
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; Before we jump to basPRINT, let's print a space
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ld a, ' '
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call stdioPutC
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jr basPRINT
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.parseError:
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; unwind the stack before returning
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pop hl ; <-- lvl 1
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ret
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basGOTO:
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ld de, SCRATCHPAD
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call rdWord
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ex de, hl
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call parseExpr
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ret nz
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call bufFind
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jr nz, .notFound
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push ix \ pop de
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; Z already set
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jr .end
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.notFound:
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ld de, 0
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; Z already unset
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.end:
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ld (BAS_PNEXTLN), de
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ret
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; evaluate truth condition at (HL) and set A to its value
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; Z for success (but not truth!)
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_basEvalCond:
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push hl ; --> lvl 1. original arg
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ld de, SCRATCHPAD
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call rdWord
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ex de, hl
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call parseTruth
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pop hl ; <-- lvl 1. restore
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ret
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basIF:
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call _basEvalCond
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ret nz ; error
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or a
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ret z
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; expr is true, execute next
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; (HL) back to beginning of args, skip to next arg
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call toSepOrEnd
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call rdSep
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ret nz
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ld de, basCmds2
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jp basCallCmds
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basWHILE:
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push hl ; --> lvl 1
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call _basEvalCond
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jr nz, .stop ; error
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or a
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jr z, .stop
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ret z
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; expr is true, execute next
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; (HL) back to beginning of args, skip to next arg
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call toSepOrEnd
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call rdSep
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ret nz
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ld de, basCmds2
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call basCallCmds
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pop hl ; <-- lvl 1
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jr basWHILE
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.stop:
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pop hl ; <-- lvl 1
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ret
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basINPUT:
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; If our first arg is a string literal, spit it
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call spitQuoted
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call rdSep
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call stdioReadLine
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call parseExpr
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ld (VAR_TBL), de
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call printcrlf
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cp a ; ensure Z
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ret
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basPEEK:
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call basDEEK
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ret nz
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; set MSB to 0
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xor a ; sets Z
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ld (VAR_TBL+1), a
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ret
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basPOKE:
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call rdExpr
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ret nz
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; peek address in IX. Save it for later
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push ix ; --> lvl 1
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call rdSep
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call rdExpr
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push ix \ pop hl
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pop ix ; <-- lvl 1
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ret nz
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; Poke!
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ld (ix), l
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ret
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basDEEK:
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call rdExpr
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ret nz
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; peek address in IX. Let's peek and put result in DE
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ld e, (ix)
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ld d, (ix+1)
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ld (VAR_TBL), de
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cp a ; ensure Z
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ret
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basDOKE:
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call basPOKE
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ld (ix+1), h
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ret
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basOUT:
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call rdExpr
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ret nz
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; out address in IX. Save it for later
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push ix ; --> lvl 1
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call rdSep
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call rdExpr
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push ix \ pop hl
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pop bc ; <-- lvl 1
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ret nz
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; Out!
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out (c), l
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cp a ; ensure Z
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ret
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basIN:
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call rdExpr
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ret nz
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push ix \ pop bc
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ld d, 0
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in e, (c)
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ld (VAR_TBL), de
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; Z set from rdExpr
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ret
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basGETC:
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call stdioGetC
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ld (VAR_TBL), a
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xor a
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ld (VAR_TBL+1), a
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ret
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basPUTC:
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call rdExpr
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ret nz
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push ix \ pop hl
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ld a, l
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call stdioPutC
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xor a ; set Z
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ret
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basPUTH:
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call rdExpr
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ret nz
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push ix \ pop hl
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ld a, l
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call printHex
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xor a ; set Z
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ret
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basSLEEP:
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call rdExpr
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ret nz
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push ix \ pop hl
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.loop:
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ld a, h ; 4T
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or l ; 4T
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ret z ; 5T
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dec hl ; 6T
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jr .loop ; 12T
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basADDR:
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call rdWord
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ex de, hl
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ld de, .specialTbl
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.loop:
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ld a, (de)
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or a
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jr z, .notSpecial
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cp (hl)
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jr z, .found
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inc de \ inc de \ inc de
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jr .loop
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.notSpecial:
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; not found, find cmd. needle in (HL)
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ex de, hl ; now in (DE)
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ld hl, basCmds1
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call basFindCmd
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jr z, .foundCmd
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; no core command? let's try the find hook.
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ld ix, (BAS_FINDHOOK)
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call callIX
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ret nz
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.foundCmd:
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; We have routine addr in IX
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ld (VAR_TBL), ix
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cp a ; ensure Z
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ret
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.found:
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; found special thing. Put in "A".
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inc de
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call intoDE
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ld (VAR_TBL), de
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ret ; Z set from .found jump.
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.specialTbl:
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.db '$'
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.dw SCRATCHPAD
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.db 0
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basUSR:
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call rdExpr
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ret nz
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push ix \ pop iy
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; We have our address to call. Now, let's set up our registers.
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; HL comes from variable H. H's index is 7*2.
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ld hl, (VAR_TBL+14)
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; DE comes from variable D. D's index is 3*2
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ld de, (VAR_TBL+6)
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; BC comes from variable B. B's index is 1*2
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ld bc, (VAR_TBL+2)
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; IX comes from variable X. X's index is 23*2
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ld ix, (VAR_TBL+46)
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; and finally, A
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ld a, (VAR_TBL)
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call callIY
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basR2Var: ; Just send reg to vars. Used in basPgmHook
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; Same dance, opposite way
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ld (VAR_TBL), a
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ld (VAR_TBL+46), ix
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ld (VAR_TBL+2), bc
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ld (VAR_TBL+6), de
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ld (VAR_TBL+14), hl
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cp a ; USR never errors out
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ret
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; Command table format: Null-terminated string followed by a 2-byte routine
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; pointer.
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; direct only
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basCmds1:
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.db "list", 0
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.dw basLIST
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.db "run", 0
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.dw basRUN
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.db "clear", 0
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.dw bufInit
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; statements
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basCmds2:
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.db "print", 0
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.dw basPRINT
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.db "goto", 0
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.dw basGOTO
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.db "if", 0
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.dw basIF
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.db "while", 0
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.dw basWHILE
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.db "input", 0
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.dw basINPUT
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.db "peek", 0
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.dw basPEEK
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.db "poke", 0
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.dw basPOKE
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.db "deek", 0
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.dw basDEEK
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.db "doke", 0
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.dw basDOKE
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.db "out", 0
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.dw basOUT
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.db "in", 0
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.dw basIN
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.db "getc", 0
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.dw basGETC
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.db "putc", 0
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.dw basPUTC
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.db "puth", 0
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.dw basPUTH
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.db "sleep", 0
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.dw basSLEEP
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.db "addr", 0
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.dw basADDR
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.db "usr", 0
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.dw basUSR
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.db 0xff ; end of table
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