integrated operator recognition routine

c64/basic/engine/ad9e.frmevl.s

@@ -129,26 +129,22 @@ FRMEVL_got_value:
 
 FRMEVL_fetch_operator:
 
-	// We have a value, but this is not the end of expression. We expect
-	// a two argument operator here. First make sure we have enough space
-	// on a stack - we will surely need it
+	// We have a value, but this is not the end of expression. Check if
+	// there is an operator waiting to be served
+
+	jsr fetch_operator
+	bcs FRMEVL_calculate               // branch if operator not recognized
+
+	// We have a two-argument operator - check if there is enough stack space
+	// XXX this can probably be checked later
 
 	tsx
 	cpx #$40                           // XXX is this a safe threshold?
 	bcc_16 do_FORMULA_TOO_COMPLEX_error
 
-	// Now look for an operator
-	// XXX for now only addition operator is implemented
+	// XXX check the priorities - either push to stack, or execute it immediately
 
-	jsr fetch_character
-	cmp #$AA                           // check for a plus operator 
-	beq FRMEVL_push_value_operator
-
-	// Something unknown - consider this the end of expression
-
-	jsr unconsume_character
-
-	// FALTROUGH
+	bcs FRMEVL_push_value_operator     // branch always
 
 FRMEVL_calculate:                      // this is the exit point for the operators
 
@@ -168,7 +164,11 @@ FRMEVL_done:
 
 FRMEVL_push_value_operator:
 
-	// First push the return address
+	// Move the operator ID in .Y
+
+	tay
+
+	// Push the return address
 
 	lda #>(FRMEVL_calculate - 1)
 	pha
@@ -204,16 +204,16 @@ FRMEVL_push_operator_address:
 	// Push the operator address to stack, in a form
 	// suitable for RTS
 
-	// XXX add support for other operators
+	// XXX add support for other operators, use .Y
 
-	lda #>(oper_add - 1)
+	lda operator_jumptable_hi - 1, y
 	pha
-	lda #<(oper_add - 1)
+	lda operator_jumptable_lo - 1, y
 	pha
 
 	// Push operator priority
 
-	lda #$01                           // XXX add support for other operators
+	lda operator_priorities - 1, y
 	pha
 
 	// Continue

c64/basic/engine/fetch_operator.s

@@ -0,0 +1,93 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Fetches an operator - for the expression parser
+//
+// Note: does not recognize unary operators
+//
+
+
+fetch_operator: // XXX change the operator code to start from 0
+
+	// Retrieve the next character
+
+	jsr fetch_character
+
+	// Check if within range
+
+	sec
+	sbc #$A9
+	bcc fetch_operator_failed             // branch if below 0
+	beq fetch_operator_failed             // branch 0
+
+	cmp #$0B
+	bcs fetch_operator_failed             // branch if $0B or greater
+
+	// Now we have to recognize '>=', '<=' and '<>' operators
+
+	cmp #$08
+	beq fetch_operator_try_gteq
+
+	cmp #$0A
+	beq fetch_operator_try_lteq_neq
+
+	// FALLTROUGH
+
+fetch_operator_success:
+
+	clc
+	rts
+
+fetch_operator_failed:
+
+	sec
+	rts
+
+
+fetch_operator_try_gteq:
+
+	// Here we distinguish between '>' and '>='
+
+	jsr fetch_character
+	cmp #$B2                           // '='
+	beq !+
+
+	// This is a '>'
+
+	jsr unconsume_character
+	lda #$08
+	bne fetch_operator_success         // branch always
+!:
+	// This is a '>='
+
+	lda #$0B
+	bne fetch_operator_success         // branch always
+
+
+fetch_operator_try_lteq_neq:
+
+	// Here we distinguish between '<', '<=', and '<>'
+
+	jsr fetch_character
+	cmp #$B2                           // '='
+	beq !+
+	cmp #$B1                           // '>'
+	beq !++
+
+	// This is a '<'
+
+	jsr unconsume_character
+	lda #$0A
+	bne fetch_operator_success         // branch always
+!:
+	// This is a '<='
+
+	lda #$0C
+	bne fetch_operator_success         // branch always
+!:
+	// This is a '<>'
+
+	lda #$0D
+	bne fetch_operator_success         // branch always