/* Print names, integer and double constants from input stream */
            /*============= 1. The definitions section ====================*/
%{
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
%}

            /* Macro defining the exponent in double constant */
EXP     ((E|e)("+"|"-")?[0-9]+)

%%
            /*============= 2. The rules (regular expressions) section ======*/

[a-zA-Z][a-zA-Z0-9]*            {
                printf("name: %s\n", yytext);
            }
(" "|\t|\n|\r\n)*   {}                  /* Skip space */

            /* Integer constant */
[0-9]+      {
                printf("integer constant: %s\n", yytext);
            }

            /* Double constant may be in one of the following 3 forms:        */
            /* 1) .5, .5e-20, 1.2, 123.456E+10 (mandatory point and fraction) */
            /* 2) 1., 123.e+10, 0.2E-20, 35.3  (mandatory integer and point)  */
            /* 3) 1e+10, 2e20, 1E-12        (mandatory integer and exponent)  */
            /* The expression for double is the union "|" of 3 subexpressions */
([0-9]*"."[0-9]+{EXP}?)|([0-9]+"."[0-9]*{EXP}?)|([0-9]+{EXP}) {
                printf("double constant: %s\n", yytext);
            }

.           {} /* Any other character */

%%
            /*============= The user programs section ===================*/

int main() {
    yylex();
    return 0;
}

int yywrap() { return 1; }      /* Stop at end of file */