From: "ara.t.howard" <ara.t.howard@...>
Date: 2007-11-17T07:06:50+09:00
Subject: Re: Yielding an object and caring about the result: the cousin of Object#tap


On Nov 15, 2007, at 1:05 PM, Robert Klemme wrote:

> Interesting point although I am not sure whether #as is really  
> functional (and thus, whether Daniel's remark is really close to  
> the mark).  If I think of functional programming paradigm first  
> item that comes to mind is lack of side effects (other than IO  
> probably).  Here, #as just enables method chaining in a single  
> statement where you would otherwise need multiple statements.  From  
> my point of view this is not functional vs. non functional.  In the  
> end it's mainly a question of scoping: whether you need multiple  
> local variables in the current scope or can achieve the same with  
> temporaries in nested and thus smaller scopes.  FC has stressed  
> this point several times.

i guess it reminds of 'let' a little...

this sprang to mind:

cfp:~ > cat a.rb
class Object
   def let *a, &b
     Let.evaluate *a, &b
   end

   def as local, kvs = {}, &block
     kvs.update local => self
     Let.evaluate kvs, &block
   end

   class Let
     instance_methods.each{|m| undef_method m unless m[%r/^__/]}

     Instance_eval = Object.instance_method :instance_eval
     Instance_variable_set =  
Object.instance_method :instance_variable_set

     def self.evaluate kvs = {}, &block
       let = new
       singleton_class =
         class << let
           self
         end
       instance_eval = Instance_eval.bind let
       instance_variable_set = Instance_variable_set.bind let
       singleton_class.module_eval{ kvs.keys.each{|k| attr k} }
       instance_eval.call{ kvs.each{|k,v| instance_variable_set.call  
"@#{ k }", v} }
       instance_eval.call &block
     end
   end
end


a = 40
b = 2
c = 'forty-two'

p let(:x => a, :y => b){ x + y }

p a.as(:x){ x + b }

p a.as(:x, :y => b){ x + y }

# fatal flaw
p let(:c => a, :d => b){ c + d }



cfp:~ > ruby a.rb
42
42
42
a.rb:44:in `+': can't convert Fixnum into String (TypeError)
         from a.rb:44
         from a.rb:27:in `instance_eval'
         from a.rb:27:in `call'
         from a.rb:27:in `evaluate'
         from a.rb:3:in `let'
         from a.rb:44


still - it's kind of interesting...






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