tcfail034.hs:17:13:
    Could not deduce (Integral a) arising from a use of `mod'
    from the context (Num a, Eq a)
      bound by the type signature for test :: (Num a, Eq a) => a -> Bool
      at tcfail034.hs:16:7-32
    Possible fix:
      add (Integral a) to the context of
        the type signature for test :: (Num a, Eq a) => a -> Bool
    In the first argument of `(==)', namely `(x `mod` 3)'
    In the expression: (x `mod` 3) == 0
    In an equation for `test': test x = (x `mod` 3) == 0