test0.l

%{
#include <math.h>
%}
     
DIGIT    [0-9]
ID       [a-z][a-z0-9]*
     
%%
  
{DIGIT}+    {
              printf( "An integer: %s (%d)\n", yytext, atoi( yytext ) );
            }
     
{DIGIT}+"."{DIGIT}*        {
                     printf( "A float: %s (%g)\n", yytext, atof( yytext ) );
                     }
     
if|then|begin|end|procedure|function        {
                     printf( "A keyword: %s\n", yytext );
                     }
     
{ID}        printf( "An identifier: %s\n", yytext );
     
"+"|"-"|"*"|"/"   printf( "An operator: %s\n", yytext );
     
#.*\n     /* eat up one-line comments */
     
[ \t\n]+          /* eat up whitespace */
     
.           printf( "Unrecognized character: %s\n", yytext );
     
%%
     
void main(int argc, char **argv)
{
   ++argv, --argc;  /* skip over program name */
   if ( argc > 0 )
     yyin = fopen( argv[0], "r" );
   else
     yyin = stdin;
     
   yylex();
}

yywrap() { }