'++' in mpc_lang causes segfault

[cesquivias]

I was working through Build Your Own Lisp I mistakenly put two '+' in the grammar. The program failed with a segfault.

The problem was easy to spot, but a simple error message would be preferred.

[orangeduck]

Thanks for the report! I'll look into it 👍

[orangeduck]

This should be fixed in 6af8360. Perhaps you can check for me that it is fixed in your situation?

[cesquivias]

The program no longer segfaults. Thanks!

The program now returns an error saying "Parser Undefined!" If the error could point out where in the grammar there was an error that'd be very helpful.

[orangeduck]

Hey,

You should be able to get a specific error by looking at the return of mpca_lang.

Thanks,

Dan