T4485.hs:47:15:
    Overlapping instances for EmbedAsChild
                                (IdentityT IO) (XMLGenT m0 (XML m0))
      arising from a use of `asChild'
    Matching instances:
      instance [overlap ok] (EmbedAsChild m c, m1 ~ m) =>
                            EmbedAsChild m (XMLGenT m1 c)
        -- Defined at T4485.hs:29:10
      instance [overlap ok] EmbedAsChild
                              (IdentityT IO) (XMLGenT Identity ())
        -- Defined at T4485.hs:42:10
    (The choice depends on the instantiation of `m0'
     To pick the first instance above, use -XIncoherentInstances
     when compiling the other instance declarations)
    In the expression: asChild
    In the expression: asChild $ (genElement "foo")
    In an equation for `asChild':
        asChild b = asChild $ (genElement "foo")