From: James Edward Gray II <james@...>
Date: 2007-04-17T04:25:20+09:00
Subject: Re: factorial in ruby

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