1 files changed, 31 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_run/tcrun033.hs b/testsuite/tests/typecheck/should_run/tcrun033.hs
new file mode 100644
index 0000000000..f9cf6a3faa
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+++ b/testsuite/tests/typecheck/should_run/tcrun033.hs
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+
+{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts,
+             UndecidableInstances, TypeSynonymInstances #-}
+
+-- This test made GHC 6.3 build a superclass loop, in
+-- the instance ClassA a String declaration
+
+module Main where
+
+class (Sat (a -> b -> String), ClassB b) => ClassA a b
+
+class ClassB a where
+  fun :: a -> String
+
+class Sat x where
+   sat :: x
+
+instance ClassA a b => Sat (a -> b -> String) where
+  sat = const fun
+
+instance ClassA a String
+-- Badness was that the ClassB superclass dict was loopy
+--
+-- Needs Sat (a -> String -> String), ClassB String
+-- --> ClassA a String, ClassB String
+-- and adding ClassA gives superclass ClassB.
+
+instance ClassB String where
+  fun = id
+
+main = print ((sat :: Int -> String -> String) 3 "hello")