#--
# Functor
# Copyright (c) 2004,2005 Thomas Sawyer
#
# Ruby License
#
# This module is free software. You may use, modify, and/or redistribute this
# software under the same terms as Ruby.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE.
#
# ==========================================================================
#  Revision History
# ==========================================================================
#  05-09-22  trans
#    Made a subclass of BasicObject.
#
#  05-01-10  trans
#    Ported to Mega Modules.
# ==========================================================================
#++

require 'mega/basicobject'

#:title: Functor
#
# By definition a Functor is simply a first class method, but these are common
# in the form of Method and Proc. So here a Functor is a bit more specialized
# as a 1st class _metafunction_. Essentally, a Functor can vary its behavior
# accorrding to the operation applied to it.
#
# == Synopsis
#
#   require 'mega/functor'
#
#   f = Functor.new { |op, x| x.send(op, x) }
#   f + 1  #=> 2
#   f + 2  #=> 4
#   f + 3  #=> 6
#   f * 1  #=> 1
#   f * 2  #=> 2
#   f * 3  #=> 9
#
# == Author(s)
#
# * Thomas Sawyer
#

class Functor < BasicObject
  def initialize(*obj, &func)
    @obj = obj
    @func = func
  end
  def method_missing(op, *args)
    if @obj.empty?
      @func.call(op, *args)
    else
      @func.call(op, *(@obj + args))
    end
  end
end


#  _____         _
# |_   _|__  ___| |_
#   | |/ _ \/ __| __|
#   | |  __/\__ \ |_
#   |_|\___||___/\__|
#

=begin testing

  require 'test/unit'

  class TC_Functor < Test::Unit::TestCase

    def test_function
      f = Functor.new { |op, x| x.send(op, x) }
      assert_equal( 2, f + 1 ) #=> 2
      assert_equal( 4, f + 2 ) #=> 4
      assert_equal( 6, f + 3 ) #=> 6
      assert_equal( 1, f * 1 ) #=> 1
      assert_equal( 4, f * 2 ) #=> 4
      assert_equal( 9, f * 3 ) #=> 9
    end

    def test_decoration
      f = Functor.new("A") { |op, a, x| x.send(op, a + x) }
      assert_equal( 'BAB', f + 'B' )
      assert_equal( 'CAC', f + 'C' )
      assert_equal( 'DAD', f + 'D' )
    end

  end

=end