Re: Proposal #2659: Add sortOn and friends to Data.List

On Mon, 6 Oct 2008, Jean-Philippe Bernardy wrote:

How about capturing the pattern in higher order functions?

if we define:

...

import Data.Function import Data.List

...

data Cache b a = Cache b a fromCache (Cache _ a) = a toCache f a = Cache (f a) a cache (Cache b _) = b

...

caching f g = map fromCache . g . map (toCache f)

I've already done this with plain pairs - a distinct type like Cache is of course better. See attachKey: http://darcs.haskell.org/htam/src/Useful.hs