stream-map-async.js

// map : ( Stream a, a -> b | Promise b ) => Stream b
Stream.prototype.map = function(f) { 
  let tailM, futP;

  return  this.isEmpty || this.isAbort ? this 
        : this.isCons ?
            ( tailM = this.tail.map(f),
              futP = Promise.resolve(f(this.head))
                            .then( head => Stream.Cons(head, tailM), Stream.Abort ), 
              Stream.Future(futP)) 
        : Stream.Future(
            this.promise.then( s => s.map(f), Stream.Abort ))
}

// result : Stream aResponseType
result = Stream.fromDomEvent(fetchButton, 'click').map( e => $.ajax(...) )