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-- This test checks in which way the type checker handles phantom types in
-- RULES. We would like these type variables to be generalised, but some
-- versions of GHC instantiated them to `()', which seriously limited the
-- applicability of such RULES.
module Main (main)
where
data T a = C
foo :: T a -> String
{-# NOINLINE foo #-}
foo C = "rewrite rule did NOT fire"
{-# RULES
-- this rule will not fire if the type argument of `T' is constrained to `()'
--
"foo/C" foo C = "rewrite rule did fire"
#-}
main = putStrLn $ foo (C :: T Int)
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