// bisongrammar-1.y

%{
  #include <stdio.h>
  #include <ctype.h>
  #include <stdlib.h>
  extern int yylex(void);
  extern void yyerror(const char *message);
%}

%define parse.error verbose

%%

S : 'a' T  | 'a' 'b' T ;
T : T 'a' | 'c' | U ;
U : 'c' ;

%%

void yyerror(const char *message) {
    printf("The Bison-generated parser found an error: %s\n", message);
    exit(EXIT_FAILURE);
}

// A simple scanner.
// Returns one of the tokens 'a', 'b' or 'c', or EOF. Other input is ignored.
int yylex(void) {
    int input;
    while ((input = getchar()) != 'a' && input != 'b' && input != 'c' && input != EOF)
        ;
    return input;
}

int main(void) {
    printf("Bisongrammar-1. Enter input. End with EOF (CTRL-D on Linux).\n");
    yyparse();
    printf("Done!\n");
    return EXIT_SUCCESS;
}