Represent then/else clauses as blocks.

block_if.rb

#!/usr/bin/ruby1.9.1 -Ku
# -*- mode: ruby; coding: utf-8-unix -*-

class Conditional
   class Else
      def initialize(p,v)
         @p = p
         @v = v
      end

      def else
         unless @p then
            yield
         else
            @v
         end
      end
   end

   class Then
      def initialize(p)
         @p = p
      end

      def then
         v = nil
         if @p then
            v = yield
         end
         return Else.new(@p,v)
      end
   end

   def if()
      p = yield
      return Then.new(p)
   end
end

c = Conditional.new

a = 3
b = 1

c.if{ a < b }.then{ puts "True!" }.else{ puts "False!" }
c.if{ a > b }.then{ puts "True!" }.else{ puts "False!" }

# Local Variables:
# ruby-indent-level: 3
# indent-tabs-mode: nil
# End: