testsuite/tests/typecheck/should_fail/tcfail098.hs

   1 {-# LANGUAGE UndecidableInstances #-}
   2
   3 module ShouldFail where
   4
   5 -- The constraint in the context of an instance declaration
   6 -- is ambiguous, but we have UndecidableInstances on, so
   7 -- it could conceivably be ok (we'd need OverlappingInstances
   8 -- too in this case).  So we allow it.
   9 -- See Note [The ambiguity check for type signatures] in TcMType
  10
  11 class Bar a
  12 instance Bar a => Bar Bool
  13