On 11 Jan 2008, at 2:20 PM, Andre Nathan wrote:
On Fri, 2008-01-11 at 13:27 -0200, Andre Nathan wrote:
I was wondering if laziness would make it run as if it was a single O(n) operation (get one directory entry "on demand", pass it to filter and then to insertInTree), because only one entry is used at a time, so that only the "current" entry needs to be evaluated.
I did some experiments. This for 1000 reads of the entries of a directory with 10000 entries, checking if they match ^[0-9]+$ and printing those which do (half of them).
getDirectoryEntries, filter, mapM_: 65.52s user 6.01s system 87% cpu 1:22.21 total
openDirStream, readDirStream: 39.68s user 5.69s system 95% cpu 47.746 total
getDirectoryContents, mapM_: 63.40s user 5.96s system 95% cpu 1:12.70 total
These are all known and expected. As I said, you can expect lazy versions to normally be slower than explicit loops. The question is whether 50% more time and 300% more memory has a higher cost in your case than the extra complexity and reduced modularity of the lazy code. jcc