From: Rick DeNatale <rick.denatale@...>
Date: 2008-04-24T02:47:23+09:00
Subject: Re: Ruby and object paradigm

On Wed, Apr 23, 2008 at 10:06 AM, Albert Schlef <albertschlef@gmail.com> wrote:
>  BTW, you _can_ implement if/else in Ruby using methods alone.
>
>  That smalltalk line can be written in Ruby as...
>
>  (self == 0).ifelse lambda { 1 }, lambda { self * ((self-1).factorial) }
>
>  ...if you bother to define an 'ifelse' method for Object:
>
>  class Object
>   def ifelse(true_block, false_block)
>     if self
>       true_block.call
>     else
>       false_block.call
>     end
>   end
>  end

Sort of a circular definition though.  In the spirit of the Smalltalk
implementation it would be more like:

class Object
  def if_else(true_proc, false_proc)
         true_proc.call
   end
end

class NilClass
 def if_else(true_proc, false_proc)
         false_proc.call
   end
end

class FalseClass
 def if_else(true_proc, false_proc)
         false_proc.call
   end
end


And the call would need to be something like:

   expr.if_else lambda { "True"}, lambda {"False"}

or Proc.new... if you wanted to say return from one of the legs, i.e.
the Smalltalk

   expr ifTrue:[^"True"] ifFalse:["Whatever"]

would need to be

   expr.if_else( Proc.new {return "True"}, lambda {"Whatever"})


-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/