Scala, repeat a finite list infinitely

Question

I want to use Stream class in scala to repeat a given list infinitely.

For example the list (1,2,3,4,5) I want to create a stream that gives me (1,2,3,4,5,1,2,3,4,5,1,2,3....)

So that I can wrap the take operation. I know this can be implemented in other ways, but I wanna do it this way for some reason, just humor me :)

So the idea is that with this infinite cycle created from some list, I can use take operation, and when it reaches the end of the list it cycles.

How do I make a stream which simply repeats a given list?

Answer 1

Very similar to @Eastsun's, but a bit more intention revealing. Tested in Scala 2.8.

scala> val l  = List(1, 2, 3)
l: List[Int] = List(1, 2, 3)

scala> Stream.continually(l.toStream).flatten.take(10).toList
res3: List[Int] = List(1, 2, 3, 1, 2, 3, 1, 2, 3, 1)

Alternatively, with Scalaz:

scala> import scalaz._
import scalaz._

scala> import Scalaz._
import Scalaz._

scala> val l = List(1, 2, 3)
l: List[Int] = List(1, 2, 3)

scala> l.toStream.repeat[Stream].join.take(10).toList
res7: List[Int] = List(1, 2, 3, 1, 2, 3, 1, 2, 3, 1)

Answer 2

An alternative method is concatenating the .toStream of the input with itself recursively. That is,

scala> def xs: Stream[Int] = List(1, 2, 3).toStream #::: xs
xs: Stream[Int]

scala> xs.take(10).toList
res1: List[Int] = List(1, 2, 3, 1, 2, 3, 1, 2, 3, 1)