I am trying to use Flex to parse 'C' source code. Unfortunately I am getting the error "expected identifier or '(' before '{' token" on lines 1,12,13,14... . Any ideas why?

    %{

    %}
    digit [0-9]
    letter [a-zA-Z]
    number (digit)+
    id (letter|_)(letter|digit|_)*
    integer (int)
    character (char)
    comma [,]
    %%
    {integer} {return INT;}
    {character} {return CHAR;}
    {number} {return NUM;}
    {id} {return IDENTIFIER;}
    {comma} {return ',';}
    [-+*/] {return *yytext;}
    . {}
    %%
    main()
    {
       yylex();
    }

The corresponding flex file is as shown below:

%{
#include <ctype.h>
#include <stdio.h>
#include "myhead.h"
#include "mini.l"
#define YYSTYPE double
# undef fprintf
%}

%token INT
%token CHAR
%token IDENTIFIER
%token NUM
%token ','
%left '+' '-'
%left '*' '/'
%right UMINUS

%%

lines:lines expr '\n' {printf("%g\n",$2);}
      |lines '\n'
      |D
      |     
      ;
expr :expr '*' expr {$$=$1*$3;}
     |expr '/' expr {$$=$1/$3;}
     |expr '+' expr {$$=$1+$3;}
     |expr '-' expr {$$=$1+$3;}
     |'(' expr ')' {$$=$2;}
     |'-' expr %prec UMINUS {$$=-$2;}
     |IDENTIFIER {}
     |NUM   {}  
     ;
T    :INT {}
     |CHAR {}
     ;
L    :L ',' IDENTIFIER {}
     |IDENTIFIER {}
     ;
D    :T L {printf("T is %g, L is %g",$1,$2);}
     ;

%%
/*void yyerror (char *s)
{
  fprintf (stderr, "%s\n", s);
}  
*/  

I am compiling the generated code using the command: gcc my_file.c -ly