testsuite/tests/typecheck/should_fail/T8883.stderr


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T8883.hs:20:1: error:
    • Non type-variable argument in the constraint: Functor (PF a)
      (Use FlexibleContexts to permit this)
    • When checking the inferred type
        fold :: forall a b.
                (Regular a, Functor (PF a)) =>
                (PF a b -> b) -> a -> b