Add streams in Scala

Question

I see at least two different implementations:

def add_streams(s1:Stream[Int], s2:Stream[Int]): Stream[Int] =
  Stream.cons(s1.head + s2.head, add_stream(s1.tail, s2.tail))

def add_streams(s1:Stream[Int], s2:Stream[Int]) =
  (s1 zip s2) map {case (x,y) => x + y}

I guess the last one is more efficient since it is not recursive.
Is it correct? How would you code such a function ?

Debilski · Accepted Answer · 2011-12-12 17:49:09Z

5

The first version is broken as it doesn‘t check for the end of a Stream. (The streams needn’t be of different length for this to happen.) Given that, the zip version is the one to prefer.

answered Dec 12, 2011 at 17:49

Debilski

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Travis Brown · Accepted Answer · 2011-12-12 17:48:04Z

2

First of all: your implementations have different behavior when either of the streams is finite. The first will crash with a NoSuchElementException, while the second will just truncate the longer stream.

I find the latter much more expressive and elegant, anyway, although I doubt the performance difference would be noticeable in most cases.

answered Dec 12, 2011 at 17:48

Travis Brown

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