Problem Statement

Starting with a path to some directory, determine whether the directory is empty. An empty directory contains no files nor subdirectories. With Unix or Windows systems, every directory contains an entry for “.” and almost every directory contains “..” (except for a root directory); an empty directory contains no other entries.

Let's start with the solution:

fun isDirEmpty(path: string) = 
  let
    val dir = OS.FileSys.openDir path
    val dirEntryOpt = OS.FileSys.readDir dir
  in
    (
      OS.FileSys.closeDir(dir);
      case dirEntryOpt of 
        NONE => true
      | _    => false
    )
  end;