From: Dave Burt <dave@...>
Date: 2005-10-20T11:26:59+09:00
Subject: Re: Functional with Ruby


"Ara.T.Howard" <Ara.T.Howard@noaa.gov> wrote in message 
news:Pine.LNX.4.62.0510191259580.28380@harp.ngdc.noaa.gov...
> On Thu, 20 Oct 2005, Andreas Semt wrote:
>
>> Hello list,
>>
>> 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!
>
>
> harp:~ > cat a.rb
> list_sum = lambda{|*list| list.flatten!; list.empty? ? 0 : list.shift + 
> list_sum[list] }
>
> p list_sum[ 0b101000,  0b10 ]
>
> harp:~ > ruby a.rb
> 42

OK, this is the first actually functional post -- list_sum is a first-class 
function.

Here's my translation:

list_sum = Proc.new {|x, *xs| if x then x + list_sum[*xs] else 0 end }

Cheers,
Dave