concrete functor and monad transformers
#68Lift's <*> is not lazy
The <*> implementation for Lift is not lazy in the sense that in order to get access to the contents of Other, the right operand of <*> must be in the WHNF.
This is easy to fix, e.g.:
instance (Applicative f) => Applicative (Lift f) where
pure = Pure
Pure f <*> ax = f <$> ax
Other f <*> ax =
Other $ f <*>
(case ax of
Pure x -> pure x
Other y -> y
)Please see https://ro-che.info/articles/2019-03-02-lazy-validation-applicative for the motivation.
I've applied this, as I find this use convincing. My only reservation was that although all applicatives should satisfy
f <*> pure x = ($ x) <$> f, there might be some applicative for which the left side is more expensive.- status set to closed
Thanks Ross!
