[Haskell-cafe] Newbie question: Where is StackOverflow on the
lanny at cisco.com
Mon Aug 20 12:21:01 EDT 2007
Not really more efficient but plays to the language
take 10 $ foo (10^9)
take 10 $ bar (10^9)
bar wouldn't evaluate until the 10^9 was done. (And I just
ground my laptop to a halt checking that. :) foo on the other
hand would run out to 10^6 and then conveniently finish the rest
of your program waiting for the need of the other 10^9-10 values.
If you *always* needed the result of the 10^9 calculations then
tail-recursion should be better since you won't be holding onto
the evaluation frames.
Peter Verswyvelen wrote:
> Now if I understand this correctly, this just means that when writing
> something like:
> foo n = if n<0 then  else n : foo (n-1)
> bar n = aux 0  where
> aux i xs = if i>n then xs else aux (i+1) (i:xs)
> that foo is more efficient than bar because lazy evaluation of foo just puts
> the delayed computation in the "cdr" of the list, while lazy evaluation of
> bar has to keep track of all aux calls (the "closures") which gives much
> more overhead, maybe even stack overflow? Something like that?
Lanny Ripple <lanny at cisco.com>
ScmDB / Cisco Systems, Inc.
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