open System.Text

let escape_string (str : string) =
   let buf = StringBuilder(str.Length)
   let replaceOrLeave c =
      match c with
      | '\r' -> buf.Append "\\r"
      | '\n' -> buf.Append "\\n"
      | '\t' -> buf.Append "\\t"
      | '"' -> buf.Append "\\\""
      | _ -> buf.Append c
   str.ToCharArray() |> Array.iter (replaceOrLeave >> ignore)
   buf.ToString()