1 files changed, 22 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_compile/HasKey.hs b/testsuite/tests/typecheck/should_compile/HasKey.hs
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index 0000000000..8da7ee7205
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+++ b/testsuite/tests/typecheck/should_compile/HasKey.hs
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+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FunctionalDependencies #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+-- Provided by Christian Maeder; broke
+-- a pre-release GHC 7.0
+
+module HasKey where
+
+class Ord key => HasKey x key | x -> key where
+   toKey :: x -> key
+
+newtype Keyed x = Keyed { unKey :: x }
+
+lift :: (HasKey x1 key1,HasKey x2 key2)
+   => (key1 -> key2 -> a) -> (Keyed x1 -> Keyed x2 -> a)
+lift f x1 x2 = f (toKey . unKey $ x1) (toKey . unKey $ x2)
+
+instance HasKey x key => Eq (Keyed x) where
+   (==) = lift (==)
+
+instance HasKey x key => Ord (Keyed x)