begin implementing BASIC command loop

c64/basic/basic_execute_line.s

@@ -7,9 +7,41 @@
 
 basic_execute_line:	
 
+	;; Get next char of program text, even if it is hiding under a ROM or the
+	;; IO area.
+	ldx #<basic_current_statement_ptr
+	ldy #0
+	jsr peek_under_roms
+	
+	;; The checks should be done in order of frequency, so that we are as
+	;; fast as possible.
 
+	;; Space, which we can also just ignore
+	cmp #$20
+	beq basic_skip_char
+	;; End of line?
+	cmp #$00
+	beq basic_end_of_line
+	;; :, i.e., statement separator, which we can simply ignore
+	cmp #$3a
+	beq basic_skip_char
+	
 	;; If all else fails, it's a syntax error
 	ldx #10
 	jmp do_basic_error
 
 	jmp basic_main_loop
+
+basic_skip_char:
+	;; Advance basic text pointer
+	inc basic_current_statement_ptr+0
+	bne +
+	inc basic_current_statement_ptr+1
+*	jmp basic_execute_line
+	
+basic_end_of_line:
+
+	;; XXX - If not in direct mode, then advance to next line, if there is
+	;; one.
+	
+	jmp basic_main_loop