From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-10-20T13:01:58+09:00
Subject: Re: Functional with Ruby

On Thu, 20 Oct 2005, Dave Burt wrote:

>
> "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 }

nice.  still the functional vs. non is a very thin line in ruby:

   harp:~ > cat a.rb
   class << self
     def list_sum x = nil, *xs
       x ? x + list_sum(*xs) : 0
     end
   end

   list_sum = method 'list_sum'

   p list_sum[0b101000,  0b10]
   p list_sum[42]
   p list_sum[]


   harp:~ > ruby a.rb
   42
   42
   0

ps.  i'm trying to wrap my mind around ocaml attm.

regards.


-a
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