basic: add peek/poke/deek/doke commands

apps/basic/README.md

@@ -103,3 +103,14 @@ stored where specified. For example, `input x` stores the result of the
 evaluation in variable `x`. Before the variable name, a quoted string literal
 can be specified. In that case, that string will be printed as-is just before
 the prompt.
+
+**peek/deek**: Put the value at specified memory address into specified
+variable. peek is for a single byte, deek is for a word (little endian). For
+example, `peek 42 a` puts the byte value contained in memory address 0x002a
+into variable `a`. `deek 42 a` does the same as peek, but also puts the value
+of 0x002b into `a`'s MSB.
+
+**poke/doke**: Put the value of specified expression into specified memory
+address. For example, `poke 42 0x102+0x40` puts `0x42` in memory address
+0x2a (MSB is ignored) and `doke 42 0x102+0x40` does the same as poke, but also
+puts `0x01` in memory address 0x2b.

apps/basic/main.asm

@@ -267,6 +267,47 @@ basINPUT:
 	cp	a		; ensure Z
 	ret
 
+basPEEK:
+	call	basDEEK
+	ret	nz
+	ld	d, 0
+	call	varAssign
+	ret
+
+basPOKE:
+	call	rdExpr
+	ret	nz
+	; peek address in IX. Save it for later
+	push	ix		; --> lvl 1
+	call	rdSep
+	call	rdExpr
+	push	ix \ pop hl
+	pop	ix		; <-- lvl 1
+	ret	nz
+	; Poke!
+	ld	(ix), l
+	ret
+
+basDEEK:
+	call	rdExpr
+	ret	nz
+	; peek address in IX. Let's peek and put result in DE
+	ld	e, (ix)
+	ld	d, (ix+1)
+	call	rdSep
+	ld	a, (hl)
+	call	varChk
+	ret	nz		; not in variable range
+	; All good assign
+	call	varAssign
+	cp	a		; ensure Z
+	ret
+
+basDOKE:
+	call	basPOKE
+	ld	(ix+1), h
+	ret
+
 ; direct only
 basCmds1:
 	.dw	basBYE
@@ -285,4 +326,12 @@ basCmds2:
 	.db	"if", 0, 0, 0, 0
 	.dw	basINPUT
 	.db	"input", 0
+	.dw	basPEEK
+	.db	"peek", 0, 0
+	.dw	basPOKE
+	.db	"poke", 0, 0
+	.dw	basDEEK
+	.db	"deek", 0, 0
+	.dw	basDOKE
+	.db	"doke", 0, 0
 	.db	0xff, 0xff, 0xff	; end of table

apps/basic/tok.asm

@@ -85,3 +85,15 @@ rdWord:
 	pop	de
 	pop	af
 	ret
+
+; Read word from HL in SCRATCHPAD and then intepret that word as an expression.
+; Put the result in IX.
+; Z for success.
+rdExpr:
+	ld	de, SCRATCHPAD
+	call	rdWord
+	push	hl
+	ex	de, hl
+	call	parseExpr
+	pop	hl
+	ret