testsuite/tests/typecheck/should_compile/T18036.hs


1
2
3
4
5
6
7
8
9
10
11
12
13

{-# LANGUAGE InstanceSigs #-}
{-# OPTIONS_GHC -Wredundant-constraints #-}

module T18036 where

class Fold f where
    fold :: Monoid m => f m -> m

newtype Identity a = Identity a

instance Fold Identity where
    fold :: Identity a -> a
    fold (Identity a) = a