testsuite/tests/typecheck/should_fail/tcfail157.stderr


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tcfail157.hs:27:10: error:
    • Variable ‘b’ occurs more often
        in the constraint ‘E m a b’
        than in the instance head ‘Foo m (a -> ())’
      (Use UndecidableInstances to permit this)
    • In the instance declaration for ‘Foo m (a -> ())’