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{-# LANGUAGE TemplateHaskell, FlexibleInstances #-}
module TH_overlaps where
import Language.Haskell.TH
class C1 a where c1 :: a
class C2 a where c2 :: a
class C3 a where c3 :: a
[d|
instance {-# OVERLAPPABLE #-} C1 [a] where c1 = []
instance C1 [Int] where c1 = [1]
instance C2 [a] where c2 = []
instance {-# OVERLAPPING #-} C2 [Int] where c2 = [1]
instance C3 [a] where c3 = []
instance {-# OVERLAPS #-} C3 [[a]] where c3 = [[]]
instance C3 [[Int]] where c3 = [[1]]
|]
test1 :: ([Char],[Int])
test1 = (c1,c1)
test2 :: ([Char],[Int])
test2 = (c2,c2)
test3 :: ([Char],[[Char]],[[Int]])
test3 = (c3,c3,c3)
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