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{-# LANGUAGE TypeFamilies #-}
-- See Trac #1204
module ShouldCompile where
data FooC = FooC
data family T c
data instance T FooC = MkT { moo :: Int }
t1 :: Int -> T FooC
t1 i = MkT { moo = i }
t2 :: T FooC -> Int
t2 (MkT { moo = i }) = i
t3 :: T FooC -> Int
t3 m = moo m
f :: T FooC -> T FooC
f r = r { moo = 3 }
------------------------------------------------------------------------------
class D c where
data D1 c
works :: Int -> D1 c -> D1 c
buggy :: Int -> D1 c -> D1 c
buggy2 :: Int -> D1 c -> D1 c
instance D FooC where
data D1 FooC = D1F { noo :: Int }
works x d = d -- d unchanged, so OK
buggy x d@(D1F { noo = k }) =
d { noo = k + x }
buggy2 x d@(D1F { noo = k }) =
(d :: D1 FooC) { noo = k + x }
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