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{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, UndecidableInstances #-}
-- Compilation loops in GHC 6.2!
-- While LoopOfTheDay1.hs did compile and work,
-- this one loops during compilation, even though
-- there is only an innocent difference regarding T1,
-- i.e., an additional, non-recursive constructor component.
module ShouldCompile where
data T1 = T1a Int | T1b T1
class C0 x where foo :: x -> (); foo = undefined
-- foo :: C0 x => x -> ()
class C1 x y
class C1 x y => C2 x y
instance C0 Int => C1 () Int -- I1
instance C0 T1 => C1 () T1 -- I2
instance (C1 x T1, C1 x Int) => C2 x T1 -- I3
instance C1 x Int => C2 x Int -- I4
instance C2 () T1 => C0 T1 -- I5
instance C2 () Int => C0 Int -- I6
baz = foo (T1b (T1a 3))
{- Need
C0 T1
-->(I5) C2 () T1
-->(I3) C1 () T1, C1 () Int
-->(I1,I2) C0 T1, C0 Int
-->(recusive) C0 Int
-->(I6) C2 () Int
-->(I4) C1 () Int
-->(recursive) {}
-}
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