Re: [Haskell-cafe] [announcement] filtrable: class of filtrable containers

Oleg Grenrus 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