skeleton of expression evaluator is now ready

c64/basic/operators/oper_plus.s

@@ -0,0 +1,42 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+oper_plus:
+
+	// This operator can be used either with two strings, or with two floats
+	// First check whether arguments match and then choose the variant
+
+	pla
+	cmp VALTYP
+	bne_16 do_TYPE_MISMATCH_error
+
+	lda VALTYP
+	bmi oper_plus_strings
+
+	// FALLTROUGH
+
+oper_plus_floats:
+
+	// XXX implement this
+
+	jmp do_NOT_IMPLEMENTED_error
+
+oper_plus_strings:
+
+	// Pull string length
+
+	pla
+	sta __FAC2+0
+
+	// Retrieve string address
+
+	pla
+	sta __FAC2+2
+	pla
+	sta __FAC2+1
+
+	// XXX merge strings here
+
+	jmp FRMEVL_calculate