Problem Statement

Create a list of ten functions, in the simplest manner possible   (anonymous functions are encouraged),   such that the function at index   i   (you may choose to start   i   from either   0   or   1),   when run, should return the square of the index,   that is,   i 2. Display the result of running any but the last function, to demonstrate that the function indeed remembers its value.

Demonstrate how to create a series of independent closures based on the same template but maintain separate copies of the variable closed over. In imperative languages, one would generally use a loop with a mutable counter variable. For each function to maintain the correct number, it has to capture the value of the variable at the time it was created, rather than just a reference to the variable, which would have a different value by the time the function was run. See also: Multiple distinct objects

Let's start with the solution:

let () =
  let cls = Array.init 10 (fun i -> (function () -> i * i)) in
  Random.self_init ();
  for i = 1 to 6 do
    let x = Random.int 9 in
    Printf.printf " fun.(%d) = %d\n" x (cls.(x) ());
  done