Comment by gsg

Hmm, the OCaml could be a lot shorter:

    let rec fold_channel f acc chan =
      match input_line chan with
      | line -> fold_channel f (f line acc) chan
      | exception End_of_file -> acc

    let comma = Str.regexp ","

    let values_of_line line =
      List.map float_of_string (Str.split comma line)

    let sum_channel chan =
      let folder line tot = List.map2 (+.) tot (values_of_line line) in
      fold_channel folder (values_of_line (input_line chan)) chan

    let sum_and_print_file filename =
      let chan = open_in filename in
      sum_channel chan |> List.map string_of_float |> String.concat "," |> print_string;
      close_in chan

    let () =
      match Sys.argv with
      | [|_; filename|] -> sum_and_print_file filename
      | _ -> failwith "Exactly 1 filename must be given"

This is also a bit faster, and almost all of the difference is because I hoisted the Str.regexp ",". I suspect using a split-on-character operation would make a bit more difference there, but of course the spartan OCaml stdlib lacks such a function.