structure Converter =
struct
  fun endsWithDsc str =
    if String.size str >= 4 then
      let
        val size = String.size str
        val expectedExtension = String.substring (str, size - 4, 4)
      in
        expectedExtension = ".dsc"
      end
    else
      false

  fun convertFile path = ()

  fun loop (dir, rootPath) =
    case OS.FileSys.readDir dir of
      SOME path =>
        let
          val folderPath = String.concat [rootPath, "/", path]
        in
          if OS.FileSys.isDir folderPath then
            (* handle folder *)
            let val newDir = OS.fileSys.openDir folderPath
            in loop (newDir, folderPath)
            end
          else if OS.FileSys.isLink folderPath then
            (* continue looping and ignore *)
            loop (dir, rootPath)
          else
            (* handle file, if file has ".dsc" at the end *)
            let val () = if endsWithDsc path then convertFile folderPath else ()
            in loop (dir, rootPath)
            end
        end
    | NONE => OS.FileSys.closeDir dir

  fun main () =
    let
      val path = OS.FileSys.getDir ()
      val dir = OS.FileSys.openDir path
    in
      loop (dir, path)
    end
end