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OneOf? #68
Description
Feels like we probably already have a oneOf function that can make sure that not all branches are evaluated at once (to ensure efficient as-needed parsing), since using alt naively can lead to really really slow decoding, but I honestly don't know where it is. Is there something I'm missing that already implements this?:
oneOf :: forall f a
. Foldable f
=> f (Foreign -> F a)
-> Foreign
-> F a
oneOf f js = go (fromFoldable f) js
where
go (read : xs) js = do
case runExcept (read js) of
Right pv -> pure pv
Left e -> do
case runExcept (go xs js) of
Right pv' -> pure pv'
Left e' -> throwError (e <> e')
go Nil _ = do
throwError $ pure (ForeignError "No more parsers to attempt in oneOf")If not, I could PR this, but feels like it probably exists as a simple combination of some operators.
Activity
MonoidMusician commentedon Nov 18, 2017
This looks good! Perhaps you want to use
foldl(or evenfoldl1?) instead, to avoid copying the list?But yeah, it's hard ... we need laziness
dreamy sighpaf31 commentedon Nov 18, 2017
If we had a lazy
Either, we could use regularoneOf, right?MonoidMusician commentedon Nov 18, 2017
newtype Decoder = Decoder (Foreign -> F a)would probably work – just making the return type lazy would be hard to use, I think.paf31 commentedon Nov 18, 2017
Decoderdoes sound useful anyway.