[Haskell-cafe] [announcement] filtrable: class of filtrable containers
Kosyrev Serge
_deepfire at feelingofgreen.ru
Wed Feb 17 12:21:08 UTC 2016
Oleg Grenrus <oleg.grenrus at iki.fi> writes:
> And one more comment:
>
> The law:
>
> filter f = mapMaybe (liftA2 (<$) id (guard ∘ f))
>
> is very hard to understand.
>
> filter f = mapMaybe (\x -> if f x then Just x else Nothing)
Wow, the difference is simply astounding for me.
Does this monster
liftA2 (<$) id (guard ∘ f)
really stand for
\x -> if f x then Just x else Nothing
?
Is there really no simpler "compact" representation for this trivial idea in Haskell?
--
с уважениeм / respectfully,
Косырев Сергей
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