Implementation of scanLeft in Chapter 3.3 does not match behaviour of List

[Sorixelle]

"Exercise: Stream Combinators" asks:

Implement [...] scanLeft on Stream. They have the same semantics as the same methods on List, [...]

The behaviour of Lists scanLeft is as follows:

scala> def increment(x: Int, y: Int): Int = x + y
def increment(x: Int, y: Int): Int

scala> List.fill(5)(1).scanLeft(0)(increment)
val res0: List[Int] = List(0, 1, 2, 3, 4, 5)

However, using the solution provided by the book for Stream gives the following result (using the book's prior definition of ones):

scala> def increment(x: Int, y: Int): Int = x + y
def increment(x: Int, y: Int): Int

scala> ones.scanLeft(0)(increment).take(6)
val res0: List[Int] = List(1, 2, 3, 4, 5, 6)

The difference being that while List's scanLeft includes the zero value in the resulting List as-is, Stream's does not, instead applying f to zero and self.head as the first element of the resulting Stream. An implementation of scanLeft for Stream that follows the one in List could instead look like:

def scanLeft[B](zero: B)(f: (B, A) => B): Stream[B] = {
  val self = this
  new Stream[B] {
    def head: B = zero
    def tail: Stream[B] = self.tail.scanLeft(f(zero, self.head))(f)
  }
}