Hi,

The last "let" is missing its corresponding "in".
 let _ =
  let lexbuf = Lexing.from_channel stdin in
  let rec storeoriginalprogram =
    let expr = lexbuf in
    match expr with
    | EOF   -> ()
    | _     -> (add_text originalprogramcontents expr); storeoriginalprogram
  in let parseprogram = List.iter
    (fun n -> print_string n; print_string "\n";) originalprogramcontents
  in parsepreogram

You may also remove the last "let": 

let _ =
  let lexbuf = Lexing.from_channel stdin in
  let rec storeoriginalprogram =
    let expr = lexbuf in
    match expr with
    | EOF   -> ()
    | _     -> (add_text originalprogramcontents expr); storeoriginalprogram
  in 
  List.iter
    (fun n -> print_string n; print_string "\n";) originalprogramcontents

Hope this helps.
--
Benjamin Monate
CEA LIST
Head of Software Safety Lab.