Hi all,

I propose we add a strict version of <$> to base:

    -- | A strict version of 'Data.Functor.<$>' for monads.

    (<$!>) :: Monad m => (a -> b) -> m a -> m b

    f <$!> m = do

        a <- m

        return $! f a

    {-# INLINE (<$!>) #-}

    infixl 4 <$!>

It works on Monads instead of Functors as required by us inspecting the argument.

This version is highly convenient if you want to work with functors/applicatives in e.g. parser and avoid spurious thunks at the same time. I realized that it was needed while fixing large space usage (but not space-leak) issues in cassava.

I believe Edward Kmett discovered the need for it independently as well.

Deadline: 3 weeks

Cheers,

Johan

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