[Haskell-cafe] a beginner question: decorate-op-undecorate

Luke Palmer lrpalmer at gmail.com
Fri Feb 5 19:24:41 EST 2010

On Fri, Feb 5, 2010 at 10:34 AM, Aran Donohue <aran.donohue at gmail.com> wrote:
> What would be an idiomatic Haskell way to accomplish this? Currently I've
> got "liftedPartitionEithers :: [a] -> (a -> Either b c) -> ([a], [a])" which
> is my own version of partitionEithers that calls a selector first.

Since you are not using b or c anywhere else, the only thing you care
about in that Either is whether it is Left or Right.  Which makes it
seem much more like a Bool.  After this conversion, I can hoogle for
your signature.


Which gives, among other things, Data.List.partition :: (a -> Bool) ->
[a] -> ([a],[a]).

Without more details about the precise thing you want to accomplish, I
don't know what else to say.  Many idioms are about the details of the
problem, even down to argument order.


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