Yes, that'd be my suggestion. čt 26. 2. 2015 v 16:03 odesílatel David Feuer napsal:

So are you suggesting that we add these to Data.Foldable?

headMay = foldr (\x _ -> Just x) Nothing lastMay = foldl (\_ x -> Just x) Nothing On Feb 26, 2015 9:18 AM, "Petr Pudlák" wrote:

...

Hi,

today I was a bit surprised that apparently there is no easy way how to safely get the head element of `Seq` in a point-free way. Of course there is `viewl`, but it seems the data type has no folding function (something like 'foldViewL :: b -> (a -> Seq a -> b) -> b`.

Is there any existing function like `Seq a -> Maybe a` to safely retrieve the head (or last) element?

If not, I'd suggest to add

headMaybe :: (Foldable t) => t a -> Maybe a headMaybe = getFirst . foldMap (First . Just)

and similarly lastMaybe to Data.Foldable.

Thanks, Petr

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