Add many1Till to Combinators

[newlandsvalley]

No description provided.

[paf31]

Now we can also write manyTill p end = (end *> pure Nil) <|> many1Till p end.

[newlandsvalley]

Yes, but - forgive my ignorance - surely we can't mutually define manyTill and many1Till each in terms of the other can we?

[paf31]

I think we can, because many1Till only uses manyTill after p, which means the recursive call is guarded by a function (implicit in the do notation block).

[newlandsvalley]

OK - I think I see what you mean - I'd never have spotted it. I'll try it out - it certainly simplifies manyTill.

[paf31]

Looks great, thanks!

[newlandsvalley]

Thanks. I've just become a bit concerned by this, though:

  let
    target = (joinWith "" $ replicate 100000 "a") <> "b"
  assert' "manyTill should not blow the stack" $ canParse (manyTill (string "a") (string "b")) (target)

blows the call stack.

[paf31]

Yes, that's a general issue right now. It's not just this function.

[newlandsvalley]

Oh - that's good news. It's just that I saw similar tests in place for many.

[paf31]

Well, many uses Data.List.manyRec, which is stack-safe, but that's a special case. We could try to write these two functions using MonadRec, it might be an interesting exercise.

[newlandsvalley]

Hmm - looks like I need to do some more learning. Thanks again for all your help and advice.