Terminate a line with ; or ;; or in or nothing

Learning
21

For what it’s worth, I haven’t seen anyone else suggest what I normally do, which is set up all my definitions, then set up a main function for things which have side effects, then call the main function:

let a = ref 0
let b = ref 0
let f x = x + !a
let g x = x + !b
let c x = f x + g x

let main () =
  a := 1;
  b := 1;
  Printf.printf "%d\n" (c 10);
  a := 2;
  b := 2;
  Printf.printf "%d\n" (c 10)

let () = main ()

With a little practice, it’s fairly easy to tell what has side effects–usually any expression that returns unit e.g. a := 1. These can be combined together with ;.

Finally, you run the main function at the bottom to actually carry out all the side effects.

3 Likes