[SOLVED] YACC syntax error

MTK358 · 02-05-2010, 03:53 PM

I was going through this Lex/YACC tutorial:

http://ds9a.nl/lex-yacc/cvs/lex-yacc-howto.html

and I was working along with it. The Lex examples worked fine, but the YACC one quit white compiling:

Code:

$ cat test.y
%{
#include <stdio.h>
#include <string.h>
 
void yyerror(const char *str) {
	fprintf(stderr,"error: %s\n",str);
}
 
int yywrap() {
	return 1;
} 
  
main() {
	yyparse();
} 
%}

%token NUMBER STATE TOKHEAT TOKTEMP

commands:
	| commands command
	;

command:
	heat_switch
	|
	temp_set
	;

heat_switch:
	TOKHEAT STATE
	{
		printf("\tHeat turned on|off\n");
	}
	;

temp_set:
	TOKTEMP NUMBER
	{
		printf("\tTemperature Set\n");
	}
	;

$ bison -d test.y
test.y:20.1-8: syntax error, unexpected identifier:

What should I do?

irmin · 02-05-2010, 04:01 PM

You missed the '%%' between the %token-line and your rules.

Code:

%token NUMBER STATE TOKHEAT TOKTEMP

commands:
	| commands command
	;

turn to

Code:

%token NUMBER STATE TOKHEAT TOKTEMP

%%

commands:
	| commands command
	;

%% is used to separate the sections of the grammar file.

MTK358 · 02-05-2010, 04:10 PM

Great, it works now!

The tutorial had the file split into several pieces, that was a bit confusing.

MTK358 · 02-05-2010, 04:12 PM

Code:

$ cat test.l
%{
#include <stdio.h>
#include "y.tab.h"
%}

%%
heat   return TOKHEAT;
temp   return TOKTEMP;
on|off return STATE;
[0-9]+ return NUMBER;
%%

$ cat test.y
%{
#include <stdio.h>
#include <string.h>
 
void yyerror(const char *str) {
	fprintf(stderr,"error: %s\n",str);
}
 
int yywrap() {
	return 1;
} 
  
main() {
	yyparse();
} 
%}

%token NUMBER STATE TOKHEAT TOKTEMP

%%

commands:
	| commands command
	;

command:
	heat_switch
	|
	temp_set
	;

heat_switch:
	TOKHEAT STATE
	{
		printf("\tHeat turned on|off\n");
	}
	;

temp_set:
	TOKTEMP NUMBER
	{
		printf("\tTemperature Set\n");
	}
	;

$ bison -d test.y
$ flex test.l
$ gcc lex.yy.c y.tab.c -o test
gcc: y.tab.c: No such file or directory
test.l:3:19: error: y.tab.h: No such file or directory
test.l: In function ‘yylex’:
test.l:7: error: ‘TOKHEAT’ undeclared (first use in this function)
test.l:7: error: (Each undeclared identifier is reported only once
test.l:7: error: for each function it appears in.)
test.l:8: error: ‘TOKTEMP’ undeclared (first use in this function)
test.l:9: error: ‘STATE’ undeclared (first use in this function)
test.l:10: error: ‘NUMBER’ undeclared (first use in this function)

Now gcc doesn't compile!

irmin · 02-05-2010, 04:20 PM

Note that bison is not yacc. The option -d instructs bison to create a header file containing all token definitions, but this header file is called "test.h" in your case. To get yacc behaviour call bison as:

Code:

bison -d -y test.y

MTK358 · 02-05-2010, 04:54 PM

Good. Everything works now.