Cool article but I think the write-up no longer matches the actual code. Snippets in the article use `*p->p` a lot. The *p is a parser struct defined above as

  struct parser {
    const char* s;
    int pos;
    struct grid* g;
  };

Notice there is no `p` member within. Assume the author meant `*p->pos`? And indeed if you look at the code in github the parser struct is defined as

  struct parser {
    const char *s, *p;
    struct grid* g;
  };

So there's the missing `p`, even though it's no longer an int. So I presume the member variable was once known as `pos` but got renamed at some point. Some of the snippets did not get updated to match.