[Haskell-beginners] reverse 'lookup'

[Yitzchak Gale]

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