#--
# $Id: tc_monad.rb 31 2006-12-28 02:28:28Z prelude $
#
#
#     This file is part of the Prelude library that provides tools to
#     enable Haskell style functional programming in Ruby.
#
#     http://prelude.rubyforge.org 
#     
#     Copyright (C) 2006 APP Design, Inc.
#
#     This library is free software; you can redistribute it and/or
#     modify it under the terms of the GNU Lesser General Public
#     License as published by the Free Software Foundation; either
#     version 2.1 of the License, or (at your option) any later version.
#
#     This library 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.  See the GNU
#     Lesser General Public License for more details.
#
#     You should have received a copy of the GNU Lesser General Public
#     License along with this library; if not, write to the Free Software
#     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
#++

require 'prelude'

# A test class representing a genesis of a possible cloned animal
class Cloned

  include Prelude::Monad

  attr_reader :name, :mother, :father

  def initialize(n, m, f)
    @name   = n
    @mother = m
    @father = f
  end

  def to_s
    self.nil? ? 'null' : name
  end

  # Traditional versions
  def maternalGrandfather
    mother ? mother.father : nil
  end

  def mothersPaternalGrandfather
    mother ? (mother.father ? mother.father.father : nil) : nil
  end

  # Monadic versions
  def m_maternalGrandfather
    wrap >> :mother >> :father >> unwrap
  end

  def m_mothersPaternalGrandfather
    wrap.bind(:mother).bind(:father).bind(:father).unwrap
  end
end # Cloned

class TestMonad < Test::Unit::TestCase

  def setup
    @grandgrandpa = Cloned.new('Grandgrandpa',     nil,           nil)
    @grandma      = Cloned.new('Grandma',          nil, @grandgrandpa)
    @grandpa      = Cloned.new('Grandpa',          nil,           nil)
    @daddy        = Cloned.new('Daddy',       @grandma,           nil)
    @mommy        = Cloned.new('Mommy',            nil,      @grandpa)
    @sheep        = Cloned.new('Dolly',         @mommy,        @daddy)
  end # setup

  def teardown
    # Nothing
  end # teardown

  def test_monad
    result = [nil, nil]
    expect = [nil, nil]
    
    assert_equal(expect, result)
  end

  def test_no_bind
    result = @sheep.maternalGrandfather
    expect = @grandpa
    
    assert_equal(expect, result)

    result = @sheep.mothersPaternalGrandfather
    expect = nil
    
    assert_equal(expect, result)
  end

  def test_bind
    # Wrap and >>
    result = @sheep.wrap >> :mother >> :father >> @sheep.unwrap
    expect = @grandpa
    
    assert_equal(expect, result)

    # Wrap and bind
    result = @sheep.wrap.bind(:mother).bind(:father).bind(:father).unwrap
    expect = nil
    
    assert_equal(expect, result)

    # Auto-wrap and >>
    result = @sheep >> :mother >> :father >> @sheep.unwrap
    expect = @grandpa
    
    assert_equal(expect, result)

    # Auto-wrap and bind
    result = @sheep.bind(:mother).bind(:father).bind(:father).unwrap
    expect = nil
    
    assert_equal(expect, result)
  end

end # TestMonad