basic: add input command

apps/basic/README.md

@@ -95,3 +95,10 @@ by the next, and so on).
 **if**. If specified condition is true, execute the rest of the line. Otherwise,
 do nothing. For example, `if 2>1 print 12` prints `12` and `if 2<1 print 12`
 does nothing. The argument for this command is a "thruth expression".
+
+**input**. Prompts the user for a numerical value and puts that value in the
+specified variable. The prompted value is evaluated as an expression and then
+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.

apps/basic/main.asm

@@ -250,6 +250,23 @@ basIF:
 	ld	de, basCmds2
 	jp	basCallCmd
 
+basINPUT:
+	; If our first arg is a string literal, spit it
+	call	spitQuoted
+	call	rdSep
+	ld	a, (hl)
+	call	varChk
+	ret	nz		; not in variable range
+	push	af		; --> lvl 1. remember var index
+	call	stdioReadLine
+	call	parseExpr
+	push	ix \ pop de
+	pop	af		; <-- lvl 1. restore var index
+	call	varAssign
+	call	printcrlf
+	cp	a		; ensure Z
+	ret
+
 ; direct only
 basCmds1:
 	.dw	basBYE
@@ -266,4 +283,6 @@ basCmds2:
 	.db	"goto", 0, 0
 	.dw	basIF
 	.db	"if", 0, 0, 0, 0
+	.dw	basINPUT
+	.db	"input", 0
 	.db	0xff, 0xff, 0xff	; end of table

apps/basic/var.asm

@@ -55,14 +55,8 @@ varTryAssign:
 	call	parseExpr	; --> number in IX
 	jr	nz, .exprErr
 	pop	af	; <-- lvl 4
-	add	a, a	; * 2 because each element is a word
-	ld	hl, VAR_TBL
-	call	addHL
-	; HL placed, write number
-	push	ix \ pop de
-	ld	(hl), e
-	inc	hl
-	ld	(hl), d
+	push	ix \ pop de	; send number to DE
+	call	varAssign
 	xor	a	; ensure Z
 .end:
 	pop	de	; <-- lvl 3
@@ -73,6 +67,21 @@ varTryAssign:
 	pop	af	; <-- lvl 4
 	jr	.end
 
+; Given a variable **index** in A (call varChk to transform) and a value in
+; DE, assign that value in the proper cell in VAR_TBL.
+; No checks are made.
+varAssign:
+	push	hl
+	add	a, a	; * 2 because each element is a word
+	ld	hl, VAR_TBL
+	call	addHL
+	; HL placed, write number
+	ld	(hl), e
+	inc	hl
+	ld	(hl), d
+	pop	hl
+	ret
+
 ; Check if value at (HL) is a variable. If yes, returns its associated value.
 ; Otherwise, jump to parseLiteral.
 parseLiteralOrVar: