List files in a folder tail recursively

recursiveListFiles.scala

def recursiveListFiles(file: File): Array[File] = {
  @tailrec
  def trImpl(dirs: Array[File], files: Array[File]): Array[File] = {
    if (dirs.isEmpty) {
      files
    }
    else {
      val (subdirs, moreFiles) = dirs.flatMap(_.listFiles).span(_.isDirectory)
      trImpl(subdirs, files ++ moreFiles)
    }
  }

  if (file.isDirectory) {
    trImpl(Array(file), Array())
  } else if (file.isFile) {
    Array(file)
  } else {
    Array()
  }
}

def recursiveListFilesWithFilter(file: File, filter: FilenameFilter): Array[File] = {
  @tailrec
  def trImpl2(dirs: Array[File], files: Array[File]): Array[File] = {
    if (dirs.isEmpty) files
    else {
      val (subdirs, moreFiles) = dirs.flatMap(_.listFiles(filter)).span(_.isDirectory)
      trImpl2(files ++ moreFiles, subdirs)
    }
  }

  if (file.isDirectory) {
    trImpl2(Array(file), Array())
  } else if (file.isFile) {
    Array(file)
  } else {
    Array()
  }
}