Negative Lookahead

Hi, is there an idiomatic way to write a parser that only matches if it is not followed by another parser?

const parseFoo = Parsimmon.string("foo");
const parseBar = Parsimmon.string("bar");
const parseFooNotFollowedByBar = ?;

parseFoo.then(parseBar).parse("foobar"); // should succeed
parseFooNotFollowedByBar.then(parseBar).parse("foobar"); // should fail

I suspect that lookahead could help here, but the documentation does not really help me:

Parses using parser, but does not consume what it parses. Yields an empty string.

So it does not change the input and always returns the same thing. What is the difference to () => ""?

I do know that the example could easily be rewritten in an LL1 grammar that would be more efficient to parse. I’m just wondering whether parsimmon supports the approach of not matching if something else succeeds.

[wavebeem]

I’ll add this under the name notFollowedBy to emphasize that it’s a lookahead operation.

[wavebeem]

I totally missed your comment @anko. That looks like a good feature to add.