On Mon, Mar 19, 2007 at 03:22:29PM +0000, Simon Peyton-Jones wrote:
| This reminds me of something I discovered about using strict fields in | AVL trees (with ghc). Using strict fields results in slower code than | doing the `seq` desugaring by hand.
That is bad. Can you send a test case that demonstrates this behaviour?
| If I have.. | | data AVL e = E | | N !(AVL e) e !(AVL e) | .. etc | | then presumably this.. | | case avl of N l e r -> N (f l) e r | | desugars to something like .. | | case avl of N l e r -> let l' = f l | in l' `seq` r `seq` N l' e r | | but IMO it should desugar to.. | | case avl of N l e r -> let l' = f l | in l' `seq` N l' e r
I agree. If it doesn't please let me know!
Although I have not looked into this much, My guess is it is an issue in the simplifier, normally when something is examined with a case statement, the simplification context sets its status to 'NoneOf []', which means we know it is in WHNF, but we don't have any more info about it. I would think that the solution would be to add the same annotation in the simplifier to variables bound by pattern matching on strict data types? Just a theory. I am not sure how to debug this in ghc without digging into it's code. John -- John Meacham - ⑆repetae.net⑆john⑈