Scala Stream.cons for creating streams from functions

A feature of Scala that I hadn’t used before was Stream.cons. This allows you to create a stream (essentially, a lazily evaluated list) from a function. So, for doing some work on files based on their position in the directory hierarchy, we can create a list of their parents:

def fileParents(file: File) : Stream[File] = {
  val parent = file.getParentFile
  if (parent == null) Stream.empty else 
    Stream.cons(parent, fileParents(parent))
}

and then use standard Scala functionality for filtering and finding things in lists, rather than having to write code that iterates through the parent files manually.

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