Ha! You're right! I didn't think about the laziness aspect of it. Anyway, the non tail-recursive version fixed the problem. Thanks!
On Tuesday 13 February 2007 16:32, Bernie Pope wrote: > Creighton Hogg wrote: > > On 2/13/07, *Duncan Coutts* <[EMAIL PROTECTED] > > <mailto:[EMAIL PROTECTED]>> wrote: > > > > On Tue, 2007-02-13 at 15:27 -0500, Jefferson Heard wrote: > > > Hi, I am running the following code against a 210 MB file in an > > > > attempt to > > > > > determine whether I should use alex or whether, since my needs > > > > are very > > > > > performance oriented, I should write a lexer of my own. I > > > > thought that > > > > > everything I'd written here was tail-recursive > > > > Isn't that exactly the problem - that it's tail recursive? You do not > > want it to be tail recursive since then it must consume the whole > > input > > before producing any output. You want it to be as lazy as possible so > > that it can start producing tokens as soon as possible without > > having to > > consume everything. > > > > > > This may be silly of me, but I feel like this is an important point: > > so you're saying that tail recursion, without strictness, doesn't run > > in constant space? > > It is an important point, and a classic space bug (see foldl in the > Prelude). > > It it not the fault of tail recursion per se, in fact tail recursion is > often important in Haskell too. > > > So for example in the case of, > > facTail 1 n' = n' > > facTail n n' = facTail (n-1) (n*n') > > The problem with this example is that it will build up an expression of > the form: > > (n1 * n2 * n3 .....) > > in the second argument. It's size will be proportional to the number of > recursive calls made (n). > > > You'll just be building a bunch of unevaluated thunks until you hit > > the termination condition? > > To fix it you will want the function to evaluate its second argument > eagerly: > > facTail n n' = facTail (n-1) $! (n*n') > Cheers, > Bernie. > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
