Implicit parameters
From HaskellWiki
The GHC manual on implicit parameters: [1].
Working example:
{-# LANGUAGE ImplicitParams #-}
import Data.List (sortBy)
sort :: (?cmp :: a -> a -> Ordering) => [a] -> [a]
sort = sortBy ?cmp
main = let ?cmp = compare in putStrLn (show (sort [3,1,2]))
