On Tue, May 5, 2009 at 3:27 PM, Luke Palmer <lrpal...@gmail.com> wrote:
> On Sun, May 3, 2009 at 11:27 AM, Tobias Olausson <tob...@gmail.com> wrote: > >> Hello! >> I have a program that is using ST.Strict, which works fine. >> However, the program needs to be extended, and to do that, >> lazy evaluation is needed. As a result of that, I have switched >> to ST.Lazy to be able to do stuff like > > >> >> foo y = do >> x <- something >> xs <- foo (y+1) >> return (x:xs) > > > As Ryan points out, this will not do what you want. But that is > incidental, not essential: > > foo y = do > x <- something > fmap (x:) $ foo (y+1) > Questioning my own reasoning, I must apologize. I was wrong, these two programs are identical and both do what you want. Any references to the state *after* the infinite chain of foos will result in _|_, but as long as "something" is the only place that state calls occur, you will be fine. I also suspect that ST.Lazy should be no less defined than ST.Strict in all cases, modulo unsafe operations of course (you aren't doing those, are you?), so you have encountered a bug. Minimize the test case and submit a bug report :-) Luke
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