On Tue, 23 Jun 2009 14:58:11 +0200, Brandon S. Allbery KF8NH
On Jun 22, 2009, at 06:03 , Ivan Uemlianin wrote:
I'm learning Haskell from a background in Python, and I'm just looking at the sort and sortBy functions in Data.List. In Python, the decorate-sort-undecorate pattern is a popular alternative to using an explicit compare function. For example, to sort a list of lists by
It's fairly common, considering that decorate-sort-undecorate is a functional programming idiom dating back to Lisp. In Haskell it's usually expressed with the decoration in a tuple such that the default sort can be used.
map snd . sort . map (\x -> (x,decorate x))
Fancier versions use arrows to make the decorate part cleaner:
map snd . sort . map (decorate &&& id)
The simplest form for e.g. sorting by length is:
sortByLength = sortBy (comparing length)
-- Met vriendelijke groet, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --