Example of a lex file

emcc.l

%option noyywrap

A     [a-zA-Z]
DIGIT [0-9]


/* 1. include other pattern definitions here, if needed. Digits maybe? */

%{
#include "tokens.h"	/* Leave this section untouched */
%}

%%
#.+     
def		     return (DEF);
if                   return (IF);
then                 return (THEN);
while                return (WHILE);
string               return (STRING);   
real                 return (REAL);  
integer              return (INTEGER);
     
{A}+	             return (ID);
\".+\"               return (STRING_CONST);
{DIGIT}+"."{DIGIT}*  return (REAL_CONST);
{DIGIT}+             return (INT_CONST);

":="                 return (ASSIGN);
">="                 return (GREATER_EQUAL);
"<="                 return (LESS_EQUAL);
"!="                 return (NOT_EQUAL); 
"+"                  return (PLUS);
";"		     return (SEMI);
":"                  return (COLON);
","                  return (COMMA);
"("                  return (LEFT_PAREN);
")"                  return (RIGHT_PAREN);
"["                  return (LEFT_SQUARE);
"]"                  return (RIGHT_SQUARE);
"{"                  return (LEFT_BRACE);
"}"                  return (RIGHT_BRACE);
"^"                  return (CARAT);
"<"                  return (LESS_THAN);
">"                  return (GREATER_THAN);
"%"                  return (MOD);
"="                  return (EQUAL);
"-"                  return (MINUS);
"*"                  return (MULT);
"/"                  return (DIVIDE);

"{"[^}\n]*"}"        
[ \t\n]+             


%%
void yyerror () 	/* Leave this section untouched */
{
	printf (" error\n");
	exit(0);
}