Standard Library report: List union

[Jon Fairbairn]

The current library report defines unionBy like this:

  unionBy eq xs ys =3D  xs ++ deleteFirstsBy eq (nubBy eq ys) xs

why does it take the nub of ys, but not xs?  I'd have expected

  unionBy eq xs ys =3D  (nubBy eq xs) ++ deleteFirstsBy eq (nubBy eq ys) =
xs

  J=F3n

-- =

J=F3n Fairbairn                                 Jon.Fairbairn@cl.cam.ac.u=
k
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