On 12 March 2010 13:13, Roman Beslik <ber...@ukr.net> wrote: > Thanks for the answer. Sorry, I can not follow all of your thoughts because > my knowledge of strictness analysis and GHC optimizations are very basic. :( > I looked into GHC code once several years ago. BTW there are a lot of papers > about strictness analysis, but I do not know which is relevant for GHC. Can > you suggest something?
There is nothing *published* (Simon has a half-written one lying around though), but the general approach is similar to that shown in "Projections for strictness analysis" at http://homepages.inf.ed.ac.uk/wadler/topics/strictness-analysis.html. Unfortunately the weird behaviour you are seeing is due to the "demand transformer" technology of GHC, which is one of the unpublished bits... > So GHC records strictness information for lambda-abstractions, not for > function types? Eta-expansion changes strictness because it adds > lambda-abstractions. It records strictness info on *binders*, and it only records strictness info about lambdas that are syntactically manifest at the binder. So you get: let f = \z. bar e_1 g = foo e_2 e_3 in e_3 (\y. baz e_4) Then f gets strictness info about one argument, g about no arguments and the (\y. baz e_4) just doesn't stand a chance of getting improved at all. Eta expansion moves lambdas towards the binders, so it makes this approximation more effective, as you say. >> 2) GHC does not seem to be eta-expanding as much as it could get away >> with. Generally eta expansion has the following effects >> > > I think it is better to go without eta-expansion. Eta-expansion (if not > optimized when compiled) do absolutely useless job. I discovered its effect > by an accident. Eta-expansion happens quite a bit in GHC right now, though I'm not sure how important it is pragmatically. Probably quite important though - you might want to look up the "state hack" for a situation where it seems to be quite necessary. Sorry that I don't have an easy answer to your problem except "eta-expand by hand"! Cheers, Max _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
