testsuite/tests/typecheck/should_fail/T16059c.stderr


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T16059c.hs:6:6: error: [GHC-91510]
    • Illegal polymorphic type: forall a1. a1
    • In the expansion of type synonym ‘Foo’
      In the type signature: f :: Foo -> a -> f
    Suggested fix: Perhaps you intended to use RankNTypes