testsuite/tests/typecheck/should_fail/tcfail125.hs

   1 {-# LANGUAGE DatatypeContexts, ExistentialQuantification #-}
   2
   3 -- Tests the "stupid theta" in pattern-matching
   4 -- when there's an existential as well
   5
   6 module ShouldCompile  where
   7
   8 data (Show a) => Obs a = forall b. LiftObs a b
   9
  10 f :: Obs a -> String    -- Needs a (Show a) context
  11 f (LiftObs _ _) = "yes"