RubyLanguage has CallWithCurrentContinuation just like SchemeLanguage, but it misses macros so you have to use a standard class:

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

 amb =Amb.new
 foo=amb.choose a,b,c..
 amb.fail if.. 

...

I hacked on what you had above and came up with this. It memoizes and checks for nils.
 
 def choices(choicelist)
  @@cont ||= []
  choicelist.each { |choice|
   callcc { |cc|
    @@cont << cc
    @@conditionCount = 0
    return choice
   }
  }
  nil
 end

 def condition(dependsOn)
  @@memo ||= {}
  @@conditionCount ||= 0
  @@conditionCount += 1
  @@memo[@@conditionCount] ||= {}
  return if @@memo[@@conditionCount][dependsOn] == true
  if dependsOn.include? nil or @@memo[@@conditionCount][dependsOn] == false or !(@@memo[@@conditionCount][dependsOn] = yield)
	@@cont.pop.call if @@cont.last
  end
 end

 def again
  @@counter ||= 0
  @@agains ||= 0
  @@agains += 1
  return if @@counter >= @@agains
  @@counter += 1
  @@agains = 0
  @@cont.last.call
 end
 
 foo = choices(1..1000)
 bar = choices(1..1000)

 condition([bar]) { bar > 10 }
 condition([bar]) { (bar % 2) == 0 }
 condition([foo]) { foo > 30 }
 condition([foo, bar]) { bar == (foo * 2) }
 
 again
 again
 again

 puts foo
 puts bar

-- spooq

----
Also see AmbSpecialForm, AmbInPython
----
CategoryRuby