endless loop in mpc_parse

[igalic]

In my attempt to extend Lispy for a double type, I created the following grammar (full source code):

        mpc_parser_t* Integer  = mpc_new("integer");
        mpc_parser_t* Double   = mpc_new("double");
        mpc_parser_t* Symbol   = mpc_new("symbol");
        mpc_parser_t* Sexpr    = mpc_new("sexpr");
        mpc_parser_t* Expr     = mpc_new("expr");
        mpc_parser_t* Lispy    = mpc_new("lispy");

  const char *grammar = 
    "                                                                                         \n\
      double   : /-?[0-9]+.[0-9]+/ | ;                                                        \n\
      integer  : /-?[0-9]+/ | ;                                                               \n\
      symbol   : '+' | '-' | '*' | '/' | '%' | '^' | \"min\" | \"max\" | \"inc\" | \"dec\" ;  \n\
      sexpr    : '(' <expr>* ')' ;                                                            \n\
      expr     : <double> | <integer> | <symbol> | <sexpr> ;                                  \n\
      lispy    : /^/ <expr>* /$/ ;                                                            \n\
    \n";

  printf("Grammar: %s\n", grammar);

  mpca_lang(MPC_LANG_DEFAULT, grammar,
      Double, Integer, Symbol, Sexpr, Expr, Lispy);

Unfortunately, this gets my program stuck in mpc_parse(); (despite running on Linux;).

[orangeduck]

Hey,

I'm not sure exactly what might be happening but I can see a few problems with your grammar.

The double and integer expressions end with a trailing or sign |. I should probably disallow this in the grammar syntax, so that is definitely a bug in mpc to allow it, but that might be breaking it.

In your double definition regex you need to escape the . symbol, which means "any character" by itself. Again this might be causing issues but I'm not sure.

Hope that fixes it. I'll look into that issue with the grammar syntax.

Thanks,

Dan

[igalic]

ACK, Thank you very much!

[orangeduck]

This should be fixed in the newest version of mpc, but ultimately I think its due to a badly formed grammar so I'm going to close this issue. I hope that is okay 👍