Assign called for each reference in gen.

date_machine.rb

#!/usr/bin/env ruby

require 'wongi-engine'
require 'uuid'

engine = Wongi::Engine.create

uuid = UUID.generate.to_sym
engine << [  uuid, :value, nil   ]
engine << [  uuid, :type, "Date" ]

uuid = UUID.generate.to_sym
engine << [  uuid, :value, nil   ]
engine << [  uuid, :type, "Date" ]

puts 'Facts:'
engine.wmes.map { |fact|
  puts fact
}
puts "\n"

engine.rule 'date rule' do

  for_all {
    has :Datum, :value, nil
    has :Datum, :type,  "Date"

    assign :OutValue do |token|
      puts 'assign OutValue'
      '2015-09-12'
    end
    assign :NewDatum do |token|
      puts 'assign NewDatum'
      UUID.generate.to_sym
    end
  }

  do! {
    gen :NewDatum, :value, :OutValue
    gen :NewDatum, :name,  "Date"
  }
end

puts 'All Facts:'
puts engine.select(:_, :_, :_)

date_machine_2.rb

#!/usr/bin/env ruby

require 'wongi-engine'
require 'uuid'

engine = Wongi::Engine.create

uuid = UUID.generate.to_sym
engine << [  uuid, :value, nil   ]
engine << [  uuid, :type, "Date" ]

uuid = UUID.generate.to_sym
engine << [  uuid, :value, nil   ]
engine << [  uuid, :type, "Date" ]

puts 'Facts:'
engine.wmes.map { |fact|
  puts fact
}
puts "\n"

value_hash = {}

engine.rule 'date rule' do

  for_all {
    has :Datum, :value, nil
    has :Datum, :type,  "Date"

    assign :OutValue do |token|
      puts 'assign OutValue'
      '2015-09-12'
    end
    assign :NewDatum do |token|
      # We save the mapping of Datum to NewDatum so we use a single
      # value in the 'gen' calls below.
      value_hash[token[:Datum]] ||= UUID.generate.to_sym
    end
  }

  do! {
    gen :NewDatum, :value, :OutValue
    gen :NewDatum, :name,  "Date"
  }
end

puts 'All Facts:'
puts engine.select(:_, :_, :_)

Output:

Facts:
{:"4aef04c0-3b79-0133-3bad-082e5f8a66ae" :value nil}
{:"4aef04c0-3b79-0133-3bad-082e5f8a66ae" :type "Date"}
{:"4aef0a70-3b79-0133-3bad-082e5f8a66ae" :value nil}
{:"4aef0a70-3b79-0133-3bad-082e5f8a66ae" :type "Date"}

assign NewDatum
assign OutValue
assign NewDatum
assign NewDatum
assign OutValue
assign NewDatum
All Facts:
{:"4aef04c0-3b79-0133-3bad-082e5f8a66ae" :value nil}
{:"4aef04c0-3b79-0133-3bad-082e5f8a66ae" :type "Date"}
{:"4aef0a70-3b79-0133-3bad-082e5f8a66ae" :value nil}
{:"4aef0a70-3b79-0133-3bad-082e5f8a66ae" :type "Date"}
{:"4aef2990-3b79-0133-3bad-082e5f8a66ae" :value "2015-09-12"}
{:"4aef2de0-3b79-0133-3bad-082e5f8a66ae" :name "Date"}
{:"4aef3250-3b79-0133-3bad-082e5f8a66ae" :value "2015-09-12"}
{:"4aef3610-3b79-0133-3bad-082e5f8a66ae" :name "Date"}

The NewDatum assign is called four times because it is referenced twice and matches against 2 sets of facts. I would like NewDatum to be the same value for each set of generated facts.

The data_machine_2.rb example is successful because a new UUID is mapped to the token[:Datum].