basic: allow printing of quoted strings

apps/basic/README.md

@@ -41,11 +41,16 @@ is kept in order of lines. Line number don't need to be sequential. You can
 keep leeway in between your lines and then insert a line with a middle number
 later.
 
+Some commands take arguments. Those are given by typing a whitespace after the
+command name and then the argument. Additional arguments are given the same way,
+by typing a whitespace.
+
 ### Numbers, expressions and variables
 
 Only 16-bit integers (unsigned for now) are supported in this BASIC. When
 printed, they're printed in decimal form. When expressing number literals, you
-can do so either in decimal (`42`), hexadecimal (`0x2a`) or binary (`0b101010`).
+can do so either in decimal (`42`), hexadecimal (`0x2a`), binary (`0b101010`)
+or char ('a', resulting in number 97).
 
 Expressions are accepted wherever a number is expected. For example,
 `print 2+3` will print `5`. Expressions can't have whitespace inside them and
@@ -75,9 +80,12 @@ with their associated line number.
 If `goto` was previously called in direct mode, we start from that line instead.
 
 **print**. Prints the result of the specified expression, then CR/LF. Can be
-given multiple arguments, separated with `,`. In that case, all arguments are
+given multiple arguments. In that case, all arguments are printed separately
-printed separately with a space in between. For example, `print 12 13` prints
+with a space in between. For example, `print 12 13` prints `12 13<cr><lf>`
-`12 13<cr><lf>`
+
+Unlike anywhere else, the `print` command can take a string inside a double
+quote. That string will be printed as-is. For example, `print "foo" 40+2` will
+print `foo 42`.
 
 **goto**. Make the next line to be executed the line number specified as an
 argument. Errors out if line doesn't exist. Argument can be an expression. If

apps/basic/glue.asm

@@ -20,6 +20,7 @@
 .inc "lib/fmt.asm"
 .equ	EXPR_PARSE	parseLiteralOrVar
 .inc "lib/expr.asm"
+.inc "basic/util.asm"
 .inc "basic/parse.asm"
 .inc "basic/tok.asm"
 .equ	VAR_RAMSTART	SCRATCHPAD+SCRATCHPAD_SIZE

apps/basic/main.asm

@@ -176,21 +176,31 @@ basRUN:
 	ret
 
 basPRINT:
+	; Do we have arguments at all? if not, it's not an error, just print
+	; crlf
+	ld	a, (hl)
+	or	a
+	jr	z, .end
+	; Is our arg a string literal?
+	call	spitQuoted
+	jr	z, .chkAnother	; string printed, skip to chkAnother
 	ld	de, SCRATCHPAD
 	call	rdWord
 	push	hl		; --> lvl 1
 	ex	de, hl
 	call	parseExpr
-	ret	nz
+	jr	nz, .parseError
 	push	ix \ pop de
 	ld	hl, SCRATCHPAD
 	call	fmtDecimal
 	call	printstr
 	pop	hl		; <-- lvl 1
+.chkAnother:
 	; Do we have another arg?
 	call	rdSep
 	jr	z, .another
 	; no, we can stop here
+.end:
 	cp	a		; ensure Z
 	jp	printcrlf
 .another:
@@ -198,6 +208,11 @@ basPRINT:
 	ld	a, ' '
 	call	stdioPutC
 	jr	basPRINT
+.parseError:
+	; unwind the stack before returning
+	pop	hl		; <-- lvl 1
+	ret
+
 
 basGOTO:
 	ld	de, SCRATCHPAD

apps/basic/util.asm

@@ -0,0 +1,15 @@
+; Is (HL) a double-quoted string? If yes, spit what's inside and place (HL)
+; at char after the closing quote.
+; Set Z if there was a string, unset otherwise.
+spitQuoted:
+	ld	a, (hl)
+	cp	'"'
+	ret	nz
+	inc	hl
+.loop:
+	ld	a, (hl)
+	inc	hl
+	cp	'"'
+	ret	z
+	call	stdioPutC
+	jr	.loop