Re: [Chicken-users] Good way to code the equivalent to this?

[Elf]

On Mon, 25 Aug 2008, Tobia Conforto wrote:

> Elf wrote:
> > > (define a
> > >   (alist->hash-table
> > >     (let loop ((i 0))
> > >       (if (fx= 250000 i)
> > >           '()
> > >           (cons (cons (random 500000)
> > >                       (random 500000))
> > >                 (loop (fx+ 1 i)))))
> > >     =))
> >
> > for an improvement in time (surprisingly), use
> >
> > (define a
> >   (alist->hash-table
> >     (let loop ((i 0)
> >                (r '()))
> >       (if (fx= 250000 i)
> >           r
> >           (loop (fx+ 1 i)
> >                 (cons (cons (random 500000)
> >                             (random 500000))
> >                       r))))
> >     =))
> >
> > ...there are a lot more minor GCs this way
>
> Why is it surprising that the tail-recursive version performs better?  And 
> why do you say it has more GC?  Isn't it supposed to produce less garbage?

well, i say it has more cause thats what the stats said :)  the reason why 
it would be more in large cases like this is because it has to repeatedly
copy a large structure in the iterative-tail-recursion version, whereas
in the stacking recursion it just has to copy the frames onto the heap 
every so often.

-elf