1 files changed, 37 insertions, 0 deletions
diff --git a/testsuite/tests/simplCore/should_compile/T4203.hs b/testsuite/tests/simplCore/should_compile/T4203.hs
new file mode 100644
index 0000000000..9423de7a36
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+++ b/testsuite/tests/simplCore/should_compile/T4203.hs
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+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
+-- Triggered a lint error due to the specialiser
+
+module T4203 where
+
+
+newtype NonNegative a = NonNegative a
+ deriving (Eq, Num, Show)
+
+instance Num a => Arbitrary (NonNegative a) where
+  arbitrary = return (rubble (rubble 0))
+  coarbitrary = error "urk"
+
+rubble :: Num a => a -> a
+rubble 0 = 1
+rubble n = n * rubble (n-1)
+
+newtype EmptyStackSet = EmptyStackSet (NonNegative Int)
+
+instance Arbitrary EmptyStackSet where
+  arbitrary = do
+        x <- arbitrary :: Gen (NonNegative Int)
+        return $ EmptyStackSet x
+  coarbitrary = error "urk"
+
+newtype Gen a = Gen a
+
+instance Monad Gen where
+  return a    = Gen a
+  Gen m >>= k = Gen (let Gen m' = k m in m')
+
+class Arbitrary a where
+  arbitrary   :: Gen a
+  coarbitrary :: a
+
+data StackSet = StackSet