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{-# LANGUAGE DataKinds #-}
module UnsatisfiableFail3 where
import GHC.TypeError
-- This test makes sure we don't end up with duplication of error messages
-- when adding Unsatisfiable contexts to classes with superclasses.
-- Test 1: we add an Unsatisfiable context to both the class and its superclass.
class Eq a => ReflexiveEq a where
reflexiveEq :: a -> a -> Bool
reflexiveEq = (==)
instance Unsatisfiable (Text "Can't compare functions with (==)") => Eq (a -> b) where
(==) = unsatisfiable
instance Unsatisfiable (Text "Can't compare functions with reflexiveEq") => ReflexiveEq (a -> b)
type DoubleMsg = Text "Equality is not reflexive on Double"
instance Unsatisfiable DoubleMsg => ReflexiveEq Double where
reflexiveEq = unsatisfiable @DoubleMsg
foo = reflexiveEq 0 (0 :: Double)
bar = reflexiveEq (\ (x :: Int) -> x + 1)
-- Test 2: we add an Unsatisfiable context to the class, but not the superclass.
class Eq a => ReflexiveEq' a where
reflexiveEq' :: a -> a -> Bool
reflexiveEq' = (==)
instance Unsatisfiable (Text "Can't compare functions with reflexiveEq'") => ReflexiveEq' (a -> b)
instance Unsatisfiable DoubleMsg => ReflexiveEq' Double where
reflexiveEq' = unsatisfiable @DoubleMsg
foo' = reflexiveEq' 0 (0 :: Double)
bar' = reflexiveEq' (\ (x :: Int) -> x + 1)
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