(*io*)

std_in; (* is the standard input stream, namely the keyboard *)
std_out; (* is the standard output stream, namely the screen *)
output std_out "now type 4 characters\n"; (* Writes to screen *)
val x = input std_in 4; (* read 4 characters from keyboard, assign to x *)
val y = output std_out "val y = output std_out; (* look at value of y *)\n";

fun echo in_file 0 = output std_out "fini\n"
   |echo in_file lines = (output std_out (input_line in_file);
                          echo in_file (lines - 1));

(* Note that function "input_line" reads an entire line. This fn is
   supplied by ml.
   Note the use of (expression-1;expression-2; ....;expression-n) *)

val io = open_in "io"; (* That is this file!! *)
echo io 30; (* should list most, if not all, of this file on screen *)
close_in io;

fun copy from to 0 = ()
   |copy from to n = (output to (input_line from);
                      copy from to (n-1));