Using SDL, Part 4: lex and yacc

%{
/* This first section contains C code which will be included in the output
   file.
*/
#include <stdlib.h>
#include <stdio.h>
/* Since we are using C++, we need to specify the prototypes for some 
   internal yacc functions so that they can be found at link time.
*/
extern int yylex(void);
extern void yyerror(char *msg);
%}

/* This is a union of the different types of values that a token can
   take on.  In our case we'll just handle "numbers", which are of
   C int type.
*/
%union {
	int number;
}

/* These are untyped tokens which are recognized as part of the grammar */
%token AND OR EQUALS

/* Here we are, any NUMBER token is stored in the number member of the
   union above.
*/
%token  NUMBER

/* These rules all return a numeric value */
%type 
 expression
%type 
 logical_expression and or equals
%%

/* Our language consists either of a single statement or of a list of statements.
   Notice the recursivity of the rule, this allows us to have any
   number of statements in a statement list.
*/
statement_list: statement | statement_list statement
	;
	
/* A statement is simply an expression.  When the parser sees an expression
   we print out its value for debugging purposes.  Later on we'll
   have more than just expressions in our statements.
*/
statement: expression
	{ printf("Expression = %d\n", $1); }
	;
	
/* An expression can be a number or a logical expression. */
expression: NUMBER
	|   logical_expression
	;
	
/* We have a few different types of logical expressions */
logical_expression: and
	|           or
	|           equals
	;
	
/* When the parser sees two expressions surrounded by parenthesis and
   connected by the AND token, it will actually perform a C logical
   expression and store the result into $$, which is the "value" of
   this statement.
*/
and: '(' expression AND expression ')'
	{ if ( $2 && $4 ) { $$ = 1; } else { $$ = 0; } }
	;
	
or: '(' expression OR expression ')'
	{ if ( $2 || $4 ) { $$ = 1; } else { $$ = 0; } }
	;
	
equals: '(' expression EQUALS expression ')'
	{ if ( $2 == $4 ) { $$ = 1; } else { $$ = 0; } }
	;
	
%%

/* This is a sample main() function that just parses standard input
   using our yacc grammar.  It allows us to feed sample scripts in
   and see if they are parsed correctly.
*/
int main(int argc, char *argv[])
{
	yyparse();
	
}
/* This is an error function used by yacc, and must be defined */-
void yyerror(char *message)
{
	fprintf(stderr, "%s\n", message);
}

%{
/* Again, this is C code that is inserted into the beginning of the output */
#include 

#include "y.tab.h"  /* Include the token definitions generated by yacc */
%}

/* Prevent the need for linking with -lfl */
%option noyywrap

/* This next section is a set of regular expressions that describe input
   tokens that are passed back to yacc.  The tokens are defined in y.tab.h,
   which is generated by yacc.
 */
%%
\/\/.*		/* ignore comments */
-[0-9]+|[0-9]+	{ yylval.number=atoi(yytext); return NUMBER; }
[ \t\n]		/* ignore whitespace */
&&		{ return AND; }
\|\|		{ return OR; }
==		{ return EQUALS; }
.		return yytext[0];
%%

all: eval 

y.tab.c: eval.y
	yacc -d $<
	
lex.yy.c: eval.l
	lex $<
	
eval: y.tab.o lex.yy.o
	$(CC) -o $@ $^

all: eval 

%.cpp: %.y
	bison -d -o $@ $<
	
%.cpp: %.l
	flex -o$@ $<
	
yacc_eval.o: yacc_eval.cpp
lex_eval.o: lex_eval.cpp

eval: yacc_eval.o lex_eval.o
	$(CXX) -o $@ $^

extern int eval_getinput(char *buf, int maxlen);
#undef YY_INPUT
#define YY_INPUT(buf, retval, maxlen)	(retval = eval_getinput(buf, maxlen))

all: eval 

YY_PREFIX = eval_

%.cpp: %.y
	bison -p$(YY_PREFIX) -d -o $@ $<
	
%.cpp: %.l
	flex -P$(YY_PREFIX) -o$@ $<
	
yacc_eval.o: yacc_eval.cpp
lex_eval.o: lex_eval.cpp

eval: yacc_eval.o lex_eval.o
	$(CXX) -o $@ $^

function whitewash
{
        if ( $1 == "Blackbeard" ) {
                print("Pouring whitewash on Blackbeard!")
                if ( $rum >= 3 ) {
                        print("Blackbeard doesn't care anymore...")
                        mood = "happy"
                } else {
                        print($1, "says Grr....")
                        mood = "angry"
                        print("Have some more rum?")
                        ++rum
                }
        }
}

pirate = "Blackbeard"
rum = 0
mood = "angry"
print($pirate, "is walking by...")
while ( $mood == "angry" ) {
        whitewash($pirate)
}
return "there was much rejoicing"

%{
#include <stdlib.h>
#include <stdio.h>

#include "widget.h"
#include "widget_button.h"

#define PARSE_DEBUG(X)	(printf X)

#define MAX_WIDGET_DEPTH 32

static int widget_depth = -1;
static Widget *widget_stack[MAX_WIDGET_DEPTH];
static Widget *widget;

static void StartWidget(Widget *the_widget)
{
	widget_stack[widget_depth++] = widget = the_widget;
}
static void FinishWidget(void)
{
	Widget *child;
	
	--widget_depth;
	if ( widget_depth >= 0 ) {
		child = widget;
		widget = widget_stack[widget_depth];
		widget->AddChild(child);
	}
}

%}

[tokens and types skipped for brevity]

%%

widget: button
	{ FinishWidget();
	  PARSE_DEBUG(("Completed widget\n")); }
	;
	
widget_attribute:
	widget_area
	;
	
/* Widget area: x, y, width, height */
widget_area:
	AREA '{' number ',' number ',' number ',' number '}'
	{ widget->SetArea($3, $5, $7, $9);
	  PARSE_DEBUG(("Area: %dx%d at (%d,%d)\n", $7, $9, $3, $5)); }
	;
	
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/* The button widget */

button:
	button_tag '{' button_attributes '}'
	{ PARSE_DEBUG(("Completed button\n")); }
	;
	
button_tag:
	BUTTON name
	{ StartWidget(new WidgetButton($2));
	  PARSE_DEBUG(("Starting a button: %s\n", $2));
	  free($2); }
	;
	
/* The button widget attributes */
button_attributes:
	button_attribute
|	button_attributes button_attribute
	;
	
button_attribute:
	widget
|	widget_attribute
|	button_normal_image
|	button_hover_image
	;
	
button_normal_image:
	IMAGE file
	{ ((WidgetButton *)widget)->LoadNormalImage($2);
	  PARSE_DEBUG(("Button normal image: %s\n", $2));
	  free($2); }
	;
	
button_hover_image:
	HOVERIMAGE file
	{ ((WidgetButton *)widget)->LoadHoverImage($2);
	  PARSE_DEBUG(("Button hover image: %s\n", $2));
	  free($2); }
	;

background "main_menu" {
	image "main_menu"
	button "new_game" {
		area { 32, 80, 370, 64 }
		image "main_menu-new"
		hover_image "main_menu-new_hi"
		#onclick [ new_gui("new_game") ]
		onclick [ new_gui("character_screen") ]
	}
	button "load_game" {
		area { 32, 152, 370, 64 }
		image "main_menu-load"
		hover_image "main_menu-load_hi"
		onclick [ new_gui("load_game") ]
	}
	button "save_game" {
		area { 32, 224, 370, 64 }
		image "main_menu-save"
		hover_image "main_menu-save_hi"
		onclick [ new_gui("save_game") ]
	}
	button "preferences" {
		area { 32, 296, 370, 64 }
		image "main_menu-prefs"
		hover_image "main_menu-prefs_hi"
		onclick [ new_gui("preferences") ]
	}
	button "quit_game" {
		area { 32, 472, 370, 64 }
		image "main_menu-quit"
		hover_image "main_menu-quit_hi"
		onclick [ quit_game() ]
	}
}