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The following module typechecks with GHC 7.8.3, but GHC 7.10.1 gives an error:

{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleInstances #-}

module Foo where

import GHC.Exts (Any)

class MonadState s m where
  get :: m s

newtype State s a = State (s -> (s, a))

instance MonadState s (State s) where
  get = State $ \s -> (s, s)

foo :: State Any Any
foo = get

[1 of 1] Compiling Foo              ( any.hs, any.o )

any.hs:15:7:
    No instance for (MonadState Any (State Any))
      arising from a use of ‘get’
    In the expression: get
    In an equation for ‘foo’: foo = get

If I replace the uses of Any with Int, the problem goes away.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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