efficiency question

[Hal Daume III]

I don't know of a reference, but here's the basic idea:      

if you have a polymorphic type (like [a]), and it's instantiated to [Int]
(or whatever), instead of storing in memory a standard linked list 
representation like 
  
[1,2] = 1:2:[] =
  
      [1  x]   /--> [2  x]   /--> Nil
          \---/         \---/

(which would be standard), it stores it as:
  
      [x  x]   /--> [x  x]   /--> Nil
       |  \---/      |  \---/
       1             2
  
So instaed of storing 1 and 2 in the list, it stores pointers to 
them.  The reason it does this is so that it makes it easy to generate    
code for polymorhpic functions.  (,) being boxed means that instead of    
storing a pair of element, you're storing a pair of pointers.  That means
you get worse performance because you have to chase more pointers.
  
(at least that's my impression)

 - hal

--
Hal Daume III

 "Computer science is no more about computers    | hdaume@isi.edu
  than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

On Sun, 10 Feb 2002, Jorge Adriano wrote:

> On Sunday 10 February 2002 18:48, Kirsten Chevalier wrote:
> > I'd guess that it's not just that you have to apply the (,) constructor --
> > it also has to do with the fact that the tuples it's constructing here are
> > boxed.
> 
> could you elaborate a little more on that (boxed / unboxed) or provide a link 
> on the subject?
> 
> thanks
> J.A.
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