yeah, I get the purposed point of a "cut" but how I put one? Exist a basic sample? (ie: Using a peg parser how define what is a "cut"???)
expr: expr '+' API_call_here? term | termHmm, if you're using a peg parser that doesn't directly support this you can emulate it by choosing between the rhs of the cut and a production that will always match
so
expr : atom (op <cut> expr)*
expr : atom (op (expr / cut))*
cut : "XXX"?
expr : atom (op expr?)*
With this grammar:
And this input: It will first consider the first alternative (expr '+' term) but will fail to match that branch because it's missing the "term" after the "+". That's fine because there's another alternative to try (term). That alternative doesn't match either, and you'll get the error message from the last alternative that it tried (probably something like "unexpected +").But with this grammar:
Then with the same input ("5 +") it will consider the first alternative, fail to match, and then fail immediately with the error message from that first alternative (something like "missing term after +").