gistfile1.rb

class Context
  def bind(player, roleMethods)
    lambda {|(*args)|
      if args.length == 0 then return player end
      name = args[0]
      m = roleMethods[name]
      if m == nil
        m = player.method(name)
      end
      m.call *args[1..-1]
    }
  end
end


class MoneyTransfer < Context
  @@destinationMethods, @@sourceMethods = nil,nil
  def source (*args)
    @source.call args
  end
  def destination (*args)
      @destination.call args
  end
  def initialize(source,destination)
    if @@sourceMethods == nil
      @@sourceMethods = Hash.new

      @@sourceMethods[:withdraw] = lambda{ |amount|
          self.source.Movement(amount)
          self.source.log "withdrawal #{amount}"
      }
    end
    if @@destinationMethods == nil
      @@destinationMethods = Hash.new

      @@destinationMethods[:deposit] = lambda{ |amount|
             self.destination.Movement(amount)
             self.destination.log "deposited #{amount}"
         }
    end
    @source = bind source, @@sourceMethods
    @destination = bind destination, @@destinationMethods
  end
  def transfer(amount)
    source:withdraw,-amount
    destination:deposit,amount
    p (self.source:to_s)
    p (self.destination:to_s)
  end
end

class Account
  def initialize (amount,id)
    @balance = amount
    @accountid = id
  end
  def Movement(amount)
      @balance+=amount
  end
  def log(message)
    p message
  end
  def to_s
    "balance of #{@accountid}: #{@balance}"
  end
end

ctx = MoneyTransfer.new (Account.new 1000, "source"), (Account.new 1000, "destination")
ctx.transfer 100