code: function chain(source, lambda) {
      return function continuable(callback) {
          source(function continuation(err, value) {
              if (err) {
                  return callback(err)
              }
  
              lambda(value)(callback)
          })
      }
  }
docs: chain := (Continuable<A>, lambda:(A) => Continuable<B>) => Continuable<B>