[Haskell-cafe] newbie optimization question

jerzy.karczmarczuk at info.unicaen.fr jerzy.karczmarczuk at info.unicaen.fr
Sun Oct 28 14:58:14 EDT 2007

Stefan O'Rear adds to the dialogue: 

> Prabhakar Ragde wrote:
>> Jerzy Karczmarczuk wrote: 
>>> Just a trivial comment... 1. Don't speak about comparing *languages* when 
>>> you compare *algorithms*,
>>>   and in particular data structures.
>>> 2. Please, DO code the above in C, using linked lists. Compare then. 3. 
>>> Check the influence of bare printing, separated from the computation.
>> Isn't GHC clever enough to optimize away the entire computation if there is 
>> no I/O?
> Yes, but GHC is not clever enough to solve the perfect number
> classification problem.  'length' will suffice, and is prefered for most
> enumeratioon benchmarks.

My point didn't concern that point. Haskell compiler cannot change an
algorithm using lists into something which deals with indexable arrays,
usually faster. Indexing may be faster than the indirection, and the
allocation of memory costs. And there is laziness...
  That's why I proposed to check what happens if one uses linked links in
"C". Well, the follow-ups seem to suggest that the main time eater was the
overloading. I must say that I am really astonished. It is hard to believe
that such a signature can make a factor of 8. Never seen that before. 

Jerzy Karczmarczuk 

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