From: Jason Roelofs <jameskilton@...>
Date: 2007-04-17T04:35:37+09:00
Subject: Re: factorial in ruby

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On 4/16/07, James Edward Gray II <james@grayproductions.net> wrote:
>
> On Apr 16, 2007, at 1:58 PM, David Simas wrote:
>
> > On Tue, Apr 17, 2007 at 02:56:16AM +0900, Jason Roelofs wrote:
> >> No and most likely not.
> >>
> >> def fact(n)
> >>  if n == 0
> >>    1
> >>  else
> >>    n * fact(n-1)
> >>  end
> >> end
> >
> > For large enough n, this will overflow the stack.  Since Ruby doesn't
> > optimize tail-recursive functions (and the above isn't tail recursive,
> > anyway), you'd better write this function as a loop (left as an
> > exercise).
>
> >> class Integer
> >>   def fact
> >>     (2..self).inject(1) { |f, n| f * n }
> >>   end
> >> end
> => nil
> >> 0.fact
> => 1
> >> 1.fact
> => 1
> >> 10.fact
> => 3628800
> >> 10_000.fact
> => 28462596809170545189064132121198688901480514017...
>
> James Edward Gray II
>
>
I knew there was a way to use #inject here, I just didn't know how. I need
to use that function more. When does this version break Ruby?

Jason

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