> >> More importantly, understand how foldl' works and be ready to apply
> >> the same analysis and fix to any similar function.
Hi,
just a little summary of what I found, in case it might be
useful to other beginners struggling with the same problems:
* A good page is http://users.aber.ac.uk/ajc99/stricthaskell.html
* You want to think hard about which functions you want to make strict
and which are better left lazy.
* Once you have it, the DeepSeq module together with some syntactic
sugar permits you to annotate functions as strict easily:
-- strictness annotation, to be used as
-- f a x | strict a, deepStrict x = annotation
-- f a x = the_true_function_body
annotation = undefined
strict a = seq a False
deepStrict a = deepSeq a False
This worked for me, nicely. In doubt, I tried both the strict and
lazy versions...
* Optimization often changes the behavior.
* It helps to have strict versions of some common high-order
functions, for example
-- strict foldl, just as foldl'
strictFoldl :: (a -> b -> a) -> a -> [b] -> a
strictFoldl f a [] = a
strictFoldl f a (x:xs) = (strictFoldl f $! f a x) xs
strictFoldl1 f (x:xs) = strictFoldl f x xs
* I could not find any tracing tool for ghc that would enable me to
see step by step what happens. Hugs has it (look for Observe).
* The heap profiling helps but I have difficulties associating the
entities it shows with actual code of my program.
Hope this helps,
Jan
--
-------------------------------------------------------------------------
Jan Kybic <[EMAIL PROTECTED]> Odyssee, INRIA, Sophia-Antipolis, France
or <[EMAIL PROTECTED]>,tel. work +33 492 38 7589, fax 7845
http://www-sop.inria.fr/robotvis/personnel/Jan.Kybic/
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