ファイルが初期化されることを確認するため事前にマーキングする

Marking.fs

open System
open System.IO
open System.Drawing

type Kind = Text | Image

let recognize filePath =
  let ext = Path.GetExtension(filePath).ToLowerInvariant()
  match ext with
  | ".bmp"
  | ".jpg" | ".jpeg"
  | ".png"
  | ".gif"
      -> Image
  | _ -> Text

let marking filePath =
  match recognize filePath with
  | Text -> 
      use stream = new FileStream(filePath, FileMode.Append, FileAccess.Write)
      use writer = new StreamWriter(stream)
      writer.WriteLine("## MARKING ##")
      printfn "Text marking (%s)" filePath

  | Image ->
      use buffer = new MemoryStream(File.ReadAllBytes(filePath))
      use image = Bitmap.FromStream(buffer)
      use g = Graphics.FromImage(image)
      g.DrawString("## MARKING ##", SystemFonts.DefaultFont, Brushes.Red, PointF.Empty)

      image.Save(filePath)

      printfn "Image marking (%s)" filePath

let allFiles targetDir =
  let files = Directory.EnumerateFiles(targetDir, "*.*", SearchOption.AllDirectories)   
  files

[<EntryPoint>]
let main argv = 
  Environment.CurrentDirectory
  |> allFiles
  |> Seq.iter marking

  0