Is eta reduction possible?

Question

Is it possible to apply eta reduction in below case?

let normalise = filter (\\x -> Data.Char.isLetter x || Data.Char.isSpace x )

I was

Answer 1

You could take advantage of the Any monoid and the monoid instance for functions returning monoid values:

import Data.Monoid
import Data.Char

let normalise = filter (getAny . ((Any . isLetter) `mappend` (Any . isSpace)))