testsuite/tests/typecheck/should_fail/T17563.stderr


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T17563.hs:5:9: error:
    • Illegal equational constraint a b ~ a c
      (Use GADTs or TypeFamilies to permit this)
    • In the quantified constraint ‘forall (a :: * -> *). a b ~ a c’
      In the type signature: blah :: (forall a. a b ~ a c) => b -> c