skeleton of expression evaluator is now ready

Makefile

@@ -21,6 +21,7 @@ SRCDIR_BASIC   = $(SRCDIR_COMMON) \
                  c64/basic/math \
                  c64/basic/math_consts \
                  c64/basic/math_mov \
+                 c64/basic/operators \
                  c64/basic/print \
                  c64/basic/rom_revision \
                  c64/basic/wedge

c64/basic/engine/ad9e.frmevl.s

@@ -14,24 +14,62 @@
 // - INTFLG (XXX float/integer, probably)
 // - for float: FAC1
 // - for string: __FAC1 + 0 = length, __FAC1 + 1 = pointer to string
+//
+// Idea:
+// - use a stack to reorder operations, so that they can be executed
+//   in a correct order
+//
 
 // XXX finish the implementation
 
 
 FRMEVL:
 
+	// Put the sentinel to the stack
+
+	lda #$00
+	pha
+
+	// FALLTROUGH
+
+FRMEVL_loop:
+
 	// Check if end of statement
 
 	jsr end_of_statement_check
 	bcs_16 do_SYNTAX_error
 
-	// Search for opening quote
+	// There are 4 basic possibilities: a string, a float, an opening bracket, or a token
 
 	jsr fetch_character
-	cmp #$22
+	cmp #$22                           // check for opening quote
-	bne FRMEVL_fetch_float
+	beq FRMEVL_fetch_string
+	cmp #$28                           // check for opening bracket
+	beq_16 do_NOT_IMPLEMENTED_error    // XXX
+	cmp #$7F                           // check for a token
+	bcc FRMEVL_fetch_float
 
-	// FALLTROUGH
+	// Search for a value or unary operator, starting from the most probable
+	// XXX check for BASIC functions here, too
+
+	cmp #$AB                           // check for unary minus
+	beq_16 do_NOT_IMPLEMENTED_error    // XXX
+	cmp #$A8                           // check for NOT
+	beq_16 do_NOT_IMPLEMENTED_error    // XXX
+	cmp #$FF                           // check for PI
+	beq_16 do_NOT_IMPLEMENTED_error    // XXX
+	cmp #$AA                           // check for unary plus (ignore this one)    
+	beq FRMEVL_loop
+
+	// Nothing recognized
+
+	jmp do_SYNTAX_error
+
+FRMEVL_fetch_float:
+
+	// XXX implement this
+
+	jmp do_SYNTAX_error
 
 FRMEVL_fetch_string:
 
@@ -54,19 +92,100 @@ FRMEVL_fetch_string:
 
 	jsr fetch_character
 	cmp #$22
-	beq FRMEVL_done
+	beq FRMEVL_got_value
 
 	inc __FAC1 + 0
 	bne !-
 
 	jmp do_STRING_TOO_LONG_error
 
-FRMEVL_fetch_float:
+FRMEVL_got_value:
 
-	// XXX implement this
+	jsr end_of_statement_check
+	bcs FRMEVL_calculate
 
-	jmp do_SYNTAX_error
+	// FALLTROUGH
+
+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
+
+	tsx
+	cpx #$40                           // XXX is this a safe threshold?
+	bcc_16 do_FORMULA_TOO_COMPLEX_error
+
+	// Now look for an operator
+	// XXX for now only plus operator is implemented
+
+	jsr fetch_character
+	cmp #$AA                           // check for a plus operator 
+	beq_16 FRMEVL_push_value_operator
+
+	// Something unknown - consider this the end of expression
+
+	// FALTROUGH
+
+FRMEVL_calculate:                      // this is the exit point for the operators
+
+	// Now, we have to calculate all the operations; at this point we
+	// should have a value in FAC1 and (possibly) operator on the stack
+
+	pla
+	beq FRMEVL_done                    // branch if sentinel
+
+	// Priority can be ignored now - just jump to the operator
+
+	// FALLTROUGH
 
 FRMEVL_done:
 
 	rts
+
+FRMEVL_push_value_operator:
+
+	// First push the value in FAC1/ARG1
+
+	ldx VALTYP
+	bmi FRMEVL_push_string
+
+	// Push float
+
+	// XXX implement this
+
+FRMEVL_push_string:
+
+	// Push string - address, length, type
+
+	lda __FAC1+1
+	pha
+	lda __FAC1+2
+	pha
+
+	lda __FAC1+0
+	pha
+
+	txa
+	pha
+
+FRMEVL_push_operator_address:
+
+	// Push the operator address to stack, in a form
+	// suitable for RTS
+
+	// XXX add support for other operators
+
+	lda #>(oper_plus - 1)
+	pha
+	lda #<(oper_plus - 1)
+	pha
+
+	// Push operator priority
+
+	lda #$01                           // XXX add support for other operators
+	pha
+
+	// Continue
+
+	jmp FRMEVL_loop

c64/basic/engine/injest_spaces.s

@@ -3,10 +3,10 @@
 // #LAYOUT# *   *       #IGNORE
 
 //
-// Injests all spaces.
+// Injests all spaces
 //
 
-// XXX get rid of this when proper number parsing is completed
+// XXX get rid of this when proper number parsing is implemented
 
 
 injest_spaces:

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