/* Code of Figure 4.13, pages 111-112 from
   Kenneth C. Louden, Programming Languages
   Principles and Practice 2nd Edition
   Copyright (C) Brooks-Cole/ITP, 2003
*/
%{
#include <stdio.h>
%}

%%
command : expr '\n' { printf("The result is: %d\n",$1); }
        ;

expr    : expr '+' term { $$ = $1 + $3; }
        | term { $$ = $1; }
        ;

term    : term '*' factor { $$ = $1 * $3; }
        | factor { $$ = $1; }
        ;

factor  : number { $$ = $1; }
        | '(' expr ')' { $$ = $2; }
        ;

number  : number digit { $$ = 10 * $1 + $2; }
        | digit { $$ = $1; }
        ;

digit   : '0' { $$ = 0; }
        | '1' { $$ = 1; }
        | '2' { $$ = 2; }
        | '3' { $$ = 3; }
        | '4' { $$ = 4; }
        | '5' { $$ = 5; }
        | '6' { $$ = 6; }
        | '7' { $$ = 7; }
        | '8' { $$ = 8; }
        | '9' { $$ = 9; }
        ;

%%

main()
{ yyparse();
  return 0; 
}

int yylex(void)
{ static int done = 0; /* flag to end parse */
  int c;
  if (done) return 0; /* stop parse */
  c = getchar();
  if (c == '\n') done = 1; /* next call will end parse */
  return c;
}

int yyerror(char *s) 
/* allows for printing error message */
{   printf("%s\n",s);
}