On May 22, 2010, at 08:30 , Ozgur Akgun wrote:
Even though CSE usually sounds good, when you ask, they go and find obscure examples in which it causes great trouble :)
They're not actually that obscure. Most of them can be summarized thusly: anything that would cause a fold to cause a stack or heap overflow if you get the strictness wrong is likely to cause the same problems if CSE "optimizes" it, for much the same reason. And, worse, if you have CSE, the only way to avoid this would be to disable it; the current situation at least permits you to manually perform CSE via let-binding. (In particular, it's often impossible to manipulate strictness; consider computing an average over a list as sum / length ("obscure"?): the only way to avoid a large list exploding in memory usage is to pull apart "sum" and "length" and thread them together, *no* strictness annotation will help.)
-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
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