[Haskell-beginners] reverse 'lookup'

[Alex Rozenshteyn]

Incidentally (and more as a curiosity than anything else)

Prelude> :t uncurry . flip . curry $ id
uncurry . flip . curry $ id :: (b, a) -> (a, b)

On Wed, Jul 7, 2010 at 1:54 PM, Yitzchak Gale <gale at sefer.org> wrote:

> Patrick LeBoutillier wrote:
> > is there... perhaps a builtin function to flip a pair:
> >  (a, b) -> (b, a)
>
> The function
>
> swap (x, y) = (y, x)
>
> will be added to Data.Tuple in the next release
> of the base libraries. In the meantime, it is easy
> enough to define it yourself, and then, of course
>
> rlookup x = lookup x . map swap
>
> Or, you could use the find function from Data.List
> and write:
>
> rlookup x = find ((== x) . snd)
>
> Regards,
> Yitz
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-- 
         Alex R
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