On Tue, Sep 05, 2006 at 12:55:48PM +0200, Udo Stenzel wrote:
> IMHO all accumulating functions, especially foldl, State.update,
> Map.insertWith, accumArray, absolutely need a strict version, because
> the strictness cannot be recovered by the library's user.
We already have foldl'. Here's a strict version of fmap:
import Control.Applicative
import Data.Traversable
newtype Strict a = Strict a
getStrict (Strict x) = x
instance Functor Strict where
fmap f (Strict x) = Strict (f x)
-- doesn't quite satisfy the Applicative laws
instance Applicative Strict where
pure x = Strict x
Strict f <*> Strict x = Strict (f $! x)
fmap' :: Traversable f => (a -> b) -> f a -> f b
fmap' f t = getStrict (traverse (Strict . f) t)
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