How do I read in lines from a text file in OCaml?

Question

This is what I have so far. Isn\'t this all that you need? I keep getting the error \"Error: Unbound module Std\"

let r file =
    let chan = open_in file in         


        

Answer 1

Here's a recursive solution using Scanf:

let read_all_lines file_name =
  let in_channel = open_in file_name in
  let rec read_recursive lines =
    try
      Scanf.fscanf in_channel "%[^\r\n]\n" (fun x -> read_recursive (x :: lines))
    with
      End_of_file ->
        lines in
  let lines = read_recursive [] in
  let _ = close_in_noerr in_channel in
  List.rev (lines);;

Usage:

let all_lines = read_all_lines "input.txt";;

However, I'd prefer to stream line-by-line:

let make_reader file_name =
  let in_channel = open_in file_name in
  let closed = ref false in
  let read_next_line = fun () ->
    if !closed then
      None
    else
      try
        Some (Scanf.fscanf in_channel "%[^\r\n]\n" (fun x -> x))
      with
        End_of_file ->
          let _ = close_in_noerr in_channel in
          let _ = closed := true in
          None in
  read_next_line;;

Usage:

let read_next = make_reader "input.txt";;
let next_line = read_next ();;

And may be a bit of icing:

type reader = {read_next : unit -> string option};;

let make_reader file_name =
  let in_channel = open_in file_name in
  let closed = ref false in
  let read_next_line = fun () ->
    if !closed then
      None
    else
      try
        Some (Scanf.fscanf in_channel "%[^\r\n]\n" (fun x -> x))
      with
        End_of_file ->
          let _ = close_in_noerr in_channel in
          let _ = closed := true in
          None in
  {read_next = read_next_line};;

Usage:

let r = make_reader "input.txt";;
let next_line = r.read_next ();;

Hope this helps!