amb.rb

require "continuation"

# via http://c2.com/cgi/wiki?AmbInRuby
class Amb
  def initialize
   @paths = []
  end

  def choose choices
   choices.each do |choice|
     callcc do |cc|
       @paths << cc
       return choice
     end
   end
   fail
  end

  def require condition
    fail unless condition
  end

  def fail
   @paths.pop.call rescue abort "Choice tree exhausted."
  end
end

amb_math.rb

#!/usr/bin/env ruby -w
require_relative 'amb.rb'

# Generates unique Pythagorean triples
# This is where a^2 + b^c = c^2 where a, b, c are not co-prime
#
# http://en.wikipedia.org/wiki/Pythagorean_triple

def py_trip from, to
  range = from..to
  amb = Amb.new

  a = amb.choose range
  b = amb.choose range
  c = amb.choose range

  amb.require (a**2 + b**2 == c**2) &&
                a.gcd(b) == 1 &&
                b.gcd(c) == 1 &&
                a.gcd(c) == 1

  return a,b,c
end

puts py_trip ARGV[0].to_i, ARGV[1].to_i

amb_puzzle.rb

#!/usr/bin/env ruby -w
require_relative 'amb.rb'

# Baker, Cooper, Fletcher, Miller, and Smith live on different floors of an apartment house that contains only five floors.
# Baker does not live on the top floor.
# Cooper does not live on the bottom floor.
# Fletcher does not live on either the top or the bottom floor.
# Miller lives on a higher floor than does Cooper.
# Smith does not live on a floor adjacent to Fletcher's.
# Fletcher does not live on a floor adjacent to Cooper's.
# Where does everyone live?

amb = Amb.new
floors = 1..5
baker = amb.choose floors
cooper = amb.choose floors
fletcher = amb.choose floors
miller = amb.choose floors
smith = amb.choose floors

apartment = {baker: baker,
             cooper: cooper,
             fletcher: fletcher,
             miller: miller,
             smith: smith}

amb.require baker != 5 &&
  cooper != 1 &&
  fletcher != 1 && fletcher != 5 &&
  miller > cooper &&
  (smith-fletcher).abs != 1 &&
  (fletcher-cooper).abs != 1 &&
  apartment.values.uniq.length == 5

puts apartment