Re: Data.List permutations

Am Dienstag 04 August 2009 20:30:58 schrieb Slavomir Kaslev:

On Tue, Aug 4, 2009 at 9:23 PM, Daniel Fischer wrote:

Which version of ghc are you testing on? I guess, it's more recent than mine.

6.10.3. But I think if you compiled it with 6.8.*, the library code would still be faster, perhaps by a smaller margin.

...

Apparently the library code is more amenable to the optimiser (note that the actual library is faster still:

Prelude Data.List> length $ permutations [1 .. 10] 3628800 (0.49 secs, 551532812 bytes) Prelude Data.List> length $ permutations [1 .. 11] 39916800 (3.73 secs, 5953485816 bytes)

I have no idea why).

Probably because it's compiled (and not interpreted) in this case.

All my times were from compiled (with -O2) code. The question is, why does the same source code produce slower object code in module Perms than in Data.List? I suppose it's because Data.List was compiled with different command line options, but I've no idea which.