[Haskell-cafe] Newbie question: Where is StackOverflow on the Wiki?

[Lanny Ripple]

Lanny Ripple wrote:
> Not really more efficient but plays to the language implementation's 
> strengths.
> 
> Imagine
> 
>   take 10 $ foo (10^9)
> 
> and
> 
>   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 

    s/10^6/10/

That's what I get for not proof-reading after making a change 
after the first proof-read.

> 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.
> 
>   -ljr
> 
> 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?
>> Thanks,
>> Peter
>>
> 
> 

-- 
Lanny Ripple <lanny at cisco.com>
ScmDB / Cisco Systems, Inc.