Revision comparison using y combinator

Revision.rb

#!/usr/bin/ruby -w

# Revision class
# Designed to function in version comparisons, where the
# version number matches /\d+(\.\d+)*/
# Author: Chris Dawes, Aupeo GmbH <chris@aupeo.com>
# Based on original by: Hugh Sasse, De Montfort University <hgs@dmu.ac.uk>
# And using: http://weblog.raganwald.com/2007/02/guest-blogger-tom-moertel-derives-y.html

def y(&f)
    lambda { |x| x[x] } [ 
        lambda { |yf| lambda { |*args| f[yf[yf]][*args] } } ]
end

class Revision

    attr :contents
    
    def self.comp(c)
      y { |x| lambda { |a,b| as = a.split(/\./); bs = b.split(/\./); return true if as.empty? && bs.empty?; af = as.shift.to_i; bf = bs.shift.to_i; return af == bf ? x[as.join('.'), bs.join('.')] : c[af, bf] } }
    end

    def self.rev_gte(a, b)
        self.comp(lambda { |x, y| x >= y })[a, b]
    end

    def self.rev_lte(a, b)
        self.comp(lambda { |x, y| x <= y })[a, b]
    end

    def to_i
	@contents.collect { |j| j.to_i }
    end

    def to_s
	astring = @contents.collect { |j| j.to_s }
        astring.join(".")
    end

    def <(x)
       !self.class.rev_gte(self.to_s, x.to_s)
    end

    def >(x)
        !self.class.rev_lte(self.to_s, x.to_s)
    end

    def ==(x)
       !((self < x) || (self > x))
    end

    def initialize(thing)
        if thing.class == Revision
		@contents = thing.contents.dup
		# dup so we get a new copy, not a pointer to it.
	elsif thing.class == String
		result = thing.split(".").collect {|j| j.to_i}
		@contents = result
	elsif thing.class == Float
		@contents = thing.to_s.split(".").collect {|j| j.to_i}
	else
                raise "cannot initialise to #{thing}"
        end
    end

end

if __FILE__ == $0

    # Perform RubyUnit tests

    require "runit/testcase"
    require 'runit/cui/testrunner'
    require 'runit/testsuite'

    class  Testing_class < RUNIT::TestCase
        def test_a
            a = Revision.new("1.2.3")
            assert_equal([1,2,3], a.contents, "initialize failed #{a.contents}")
            a = Revision.new("2.4.8")
            b = Revision.new(a)
            assert_equal([2,4,8], b.contents, "initialize failed #{a.contents}")
            a = Revision.new(2.3)
            assert_equal([2,3], a.contents, "initialize failed #{a.contents}")
        end
        def test_equal
            a = Revision.new("1.2.1")
            b = Revision.new("1.2.1")
            assert(a == b, "supposedly identical Revisions are not.")
            a = Revision.new("2.2.2")
            b = Revision.new("2.2.1")
            assert(!(a == b), "supposedly inidentical Revisions are not.")
            a = Revision.new("1.0")
            b = Revision.new("1.0.0")
            assert((a == b), "supposedly identical Revisions are not.")
        end
        def test_less_than
            a = Revision.new("1.2.1")
            b = Revision.new("1.2.2")
            assert(a < b, " 1.2.1 not less that 1.2.2 ")
            a = Revision.new("1.2.2")
            b = Revision.new("1.3.2")
            assert(a < b, " 1.2.2 not less that 1.3.2 ")
            a = Revision.new("1.2.2")
            b = Revision.new("2.2.2")
            assert(a < b, " 1.2.2 not less that 2.2.2 ")
            a = Revision.new("1.2.3.4")
            b = Revision.new("1.2.3.5")
            assert(a < b, " 1.2.3.4 not less that 1.2.3.5 ")
            a = Revision.new("1.2.3")
            b = Revision.new("1.2.3.5")
            assert(a < b, " 1.2.3 not less that 1.2.3.5 ")
            # check comparison is numeric, not lexical
            a = Revision.new("1.2.3")
            b = Revision.new("1.12.3")
            assert(a < b, " 1.2.3 not less that 1.2.3.5 ")
        end
        def test_greater_than
            a = Revision.new("1.2.2")
            b = Revision.new("1.2.1")
            assert(a > b, " 1.2.1 not less that 1.2.2 ")
            a = Revision.new("1.3.2")
            b = Revision.new("1.2.2")
            assert(a > b, " 1.2.2 not less that 1.3.2 ")
            a = Revision.new("2.2.2")
            b = Revision.new("1.2.2")
            assert(a > b, " 1.2.2 not less that 2.2.2 ")
            a = Revision.new("1.2.3.5")
            b = Revision.new("1.2.3.4")
            assert(a > b, " 1.2.3.4 not less that 1.2.3.5 ")
            a = Revision.new("1.2.3.5")
            b = Revision.new("1.2.3")
            assert(a > b, " 1.2.3 not less that 1.2.3.5 ")
            # check comparison is numeric, not lexical
            a = Revision.new("1.12.3")
            b = Revision.new("1.2.3")
            assert(a > b, " 1.2.3 not less that 1.2.3.5 ")
        end
    end

    RUNIT::CUI::TestRunner.run(Testing_class.suite)
end