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{-# LANGUAGE DataKinds #-}
module UnsatClassMethods where
import GHC.TypeError
-- Easy version
class Cls a where
method :: a -> a -> a
instance Unsatisfiable (Text "Not allowed for Bool") => (Cls Bool)
-- Trickier version
class C a where
{-# MINIMAL (method1, method3, method4) | (method2, method3, method4) | (method1, method2, method4) #-}
method1 :: a -> a
method1 = method2
method2 :: a -> a
method2 = method1
method3 :: a -> a
method3 = method2 . method1
method4 :: a -> a -> a
instance Unsatisfiable (Text "Not allowed for Int") => (C Int) where
method3 = error "not implemented"
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