started work on LET command

src/basic/engine/fetch_variable.s

@@ -0,0 +1,84 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+fetch_variable:
+
+	// Fetch variable name
+
+	lda #$00
+	sta VARNAM+1
+
+	// Fetch the first character
+!:
+	jsr fetch_character
+	cmp #$20                           // ignore all the spaces
+	beq !-
+
+	jsr fetch_variable_is_AZ
+	bcs_16 do_SYNTAX_error
+
+	sta VARNAM+0
+
+	// Fetch the (optional) second character
+
+	jsr fetch_character
+	jsr fetch_variable_is_09_AZ
+	bcs fetch_variable_check_type
+
+	sta VARNAM+1
+
+	// Fetch the remaining variable characters - ignore them
+!:
+	jsr fetch_character
+	jsr fetch_variable_is_09_AZ
+	bcc !-
+
+	// FALLTROUGH
+
+fetch_variable_check_type:
+
+	// Encode variable type within name, as documented in:
+	// - https://sites.google.com/site/h2obsession/CBM/basic/variable-format
+
+	cmp #$24                           // '$'
+	beq fetch_variable_type_string
+	cmp #$25                           // '%'
+	beq fetch_variable_type_integer
+
+	// FALLTORUGH
+
+fetch_variable_type_float:
+
+	jsr unconsume_character
+
+#if HAS_OPCODES_65C02
+	bra fetch_variable_find_addr
+#else
+	jmp fetch_variable_find_addr
+#endif
+
+fetch_variable_type_integer:
+
+	lda VARNAM+0
+	ora #$80
+	sta VARNAM+0
+
+	// FALLTROUGH
+
+fetch_variable_type_string:
+
+	lda VARNAM+1
+	ora #$80
+	sta VARNAM+1
+	
+	// FALLTROUGH
+
+fetch_variable_find_addr:
+
+	// Now try to find variable address
+
+	// XXX
+
+	rts