stream-merge.js

// merge : (Stream a, Stream a) => Stream a
Stream.prototype.merge = function(s2) { 

  return  this.isEmpty ? s2 
        : this.isAbort ? this 
        : this.isCons  ? Stream.Cons( this.head, this.tail.merge(s2) ) 
        : ( !s2.isFuture ? 
              s2.merge(this) 
            : Stream.Future(
                Promise.race([
                  this.promise.then(s => () => s.merge(s2), Stream.Abort),
                  s2.promise.then(s => () => s.merge(this), Stream.Abort)
                ]).then(lazy => lazy())))
}


Stream.seq([1,2,3,4,5], 0, 1000)
  .merge( Stream.seq([6,7,8], 500, 1000)  )
  .log()