%option noyywrap outfile="toy_lexer.c"
/* scanner for a toy Pascal-like language                                                toy.l  */
%{
#include <math.h>           /* need this for the call to atof() below */
%}
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 );
%%

int main( int argc, char **argv ) {
    ++argv, --argc;  /* skip over program name */
    if ( argc > 0 ) yyin = fopen( argv[0], "r" );
    else            yyin = stdin;
    yylex();
    return 0;
}