On 28 February 2006 13:37, Lennart Augustsson wrote:

John Meacham wrote:

...

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.

Yes, they are optimized away when ghc actually works. :) At the moment this seems to be broken (try length[1..n] in 6.4.1).

Known bug (well, known since a few weeks ago at least). http://cvs.haskell.org/trac/ghc/ticket/683 Cheers, Simon