From: "David A. Black" <dblack@...>
Date: 2005-10-21T11:26:53+09:00
Subject: Re: Functional with Ruby

Hi --

On Thu, 20 Oct 2005, Florian Frank wrote:

> Andreas Semt wrote:
>
>> here a really simple Haskell function, which sums all elements of a list
>> (from the book "The Haskell School of Expression"):
>> --------------------------------
>> listSum [] = 0
>> listSum (x : xs) = x + listSum xs
>> --------------------------------
>> 
>> Which is the best way to say it in Ruby (functional style)? Don't use
>> 'enum.inject', please!
>> 
>
> You can abuse Ruby arrays for lists:
>
> def list_sum(l)
> case l
> when [] then 0
> else l.first + list_sum(l[1, l.size])
> end
> end
> list_sum([1,2,3]) # => 6

Just for fun I was trying to see how visually close I could get to the
Haskell.  The answer is... not very :-)  But the star operator
actually handles the x : xs list thing rather well:

   def list_sum(x,*xs)
     case xs
       when []:  x             # note: not 0 when done this way
       else x + list_sum(*xs)
     end
   end


David

-- 
David A. Black
dblack@wobblini.net