From: Jeff Wood <jeff.darklight@...>
Date: 2005-12-24T04:36:41+09:00
Subject: Re: Why not Python? (No, no, I am not a spy)

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ah, but to me that isn't completely iterative.... iterative is using a loop
within a function to make sure it and all functions it calls do not call
back up the tree...

hence:

# yes assumptions about positive integer numbers...
# complete recursive:

def factorial( x )
  return 0 if x < 1
  x * factorial( x - 1 )
end

# tail-recursive:

def factorial( x, sum =3D 1 )
  return 0 if x < 1
  factorial( ( x - 1 ), ( sum * x ) )
end

# iterative:

def factorial( x )
  sum =3D 1
  for i in (1..x).to_a
    sum *=3D i
  end
end

... anyways.

j.



On 12/23/05, Christian Neukirchen <chneukirchen@gmail.com> wrote:
>
> Jeff Wood <jeff.darklight@gmail.com> writes:
>
> > ... I believe the question was in regards to implementing factorial in =
a
> > tail-recursive manner.
> >
> > I believe the statement was:
> >
> > "I'm a complete newb to lisp, I've been reading Practical Common Lisp &
> On
> > Lisp.  I've also been working through "The little schemer" and SICP...
> I'm
> > running CMUCL under SLIME & Emacs (v21.4). ( phew ) ... I've written an
> > iterative & a normally recursive version of factorial ... Now I'm tryin=
g
> to
> > figure out how to implement it in a tail-recursive fashion ... can
> anybody
> > help me write a tail-recursive version ?? I'm not familiar with the cal=
l
> > pattern yet." ...
>
> I see, the iterative version at
>   http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-21.html#%_thm_3.9
> actually is the tail-recursive version. :-)
>
> They could have told you that, of course.
>
> > or something like that ...
> >
> > Jeff Wood
> --
> Christian Neukirchen  <chneukirchen@gmail.com>  http://chneukirchen.org
>
>


--
"Remember. Understand. Believe. Yield! -> http://ruby-lang.org"

Jeff Wood

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