Question

I am trying to read a char from a file being passed in via the stdinput in ocaml. I was wondering why I keep getting a unit when I can print_char the char that I receive in the following code. Also, I am trying to make a list of these characters which will not work as of now.

let () =
let charList = [] in 
let inchar = open_in Sys.argv.(1) in
    try 
            while true do
                let c = Char.uppercase(input_char inchar) in
                    print_char c; print_int (List.length charList);c::charList
            done
    with End_of_file -> close_in inchar;(*; print_int (List.length charList); printTest charList;*)

;;

Answer 1

Your code does not modify charList, so charList remains an empty list throughout the whole execution.

Moreover, if you define
let charList = [] then charList is immutable.

You might try something along these lines:

let () =
    let charList = ref [] in
    let inchar = open_in Sys.argv.(1) in
  try
    while true do
      let c = Char.uppercase (input_char inchar) in
            charList := c :: !charList
    done
  with End_of_file ->
        charList := List.rev !charList;
        close_in inchar;
        print_int (List.length !charList);
        List.iter print_char !charList

Some more comments:

• reading input char by char is very inefficient, use for instance input_line.
• your post mentions Sys.argv.(1) and the standard input, but those are two distinct things
• if you want to read a whole file and store it in memory, search for “ocaml input file”, there are many examples on the net, like https://groups.google.com/forum/?fromgroups#!msg/fa.caml/EEinP7-yAko/dPSaR0eOkw4J or http://camltastic.blogspot.fr/2008/09/tip-read-all-lines-from-file-most.html