On Tue, Feb 28, 2006 at 08:52:00AM +0100, Johannes Waldmann wrote:
Cale Gibbard wrote:
This is exactly why lists are so common. If people ask why lists are so common in lazy functional languages, they ought also to ask why loops are so common in imperative languages.
A loop is a sequence of actions. In FP, I don't typically have actions, rather I collect values, so I'd need several collections types, among them: sequences, and among them: classical left-biased lists.
I think the point was that lists in haskell trancend just being a collection type or a data structure. They are a generally useful tool for composing functions. And like cale said, they often subsume loops and all sorts of other control constructs. I mean, even a for loop in haskell is done as mapM action [0..10] I'd say _most_ uses of lists are deforested away because they are used to express control and dataflow and arn't actually used as persistant structures. demoting them to just being a 'collection type' would be a disservice. That they can be used as a collection is a bonus, but not their main feature. the foldr/build trick for deforesting lists is really really cool! look at ghc core, it is amazing how all your lists just disapear and are turned into clever function compositions I would have never thought of :) John -- John Meacham - ⑆repetae.net⑆john⑈