Comments on: Loops in Ocaml

By: sashang

sashang — Fri, 31 Jul 2009 10:10:23 +0000

The while, for, etc loop expressions in ocaml always have a unit return type. That’s the fundamental difference between them and a tail-recursive loop construct.

# let rec loop idx = if idx == 5 then idx else loop (idx + 1);;
val loop : int -> int =
# x;;
- : unit = ()
# let x () = for i = 0 to 5 do i done;;
Warning S: this expression should have type unit.
val x : unit -> unit =
# x ();;
- : unit = ()
# loop 0;;
- : int = 5
#

By: Jared

Jared — Wed, 15 Jul 2009 06:10:40 +0000

Ah, the while loop. I knew I had missed one! I think my brain probably glossed over it when the tutorial I was reading said it was not very useful.

Thanks.

By: Matías Giovannini

Matías Giovannini — Sun, 12 Jul 2009 02:41:48 +0000

"What other types of loops are there in Ocaml?" You can also use

whileloops, with syntax while condition do statements done. The problem with imperative loops is that there is no way to break out early of them, leading to unsightly idioms like:

begin try while true do
  (* calculations *)
  if condition then raise Exit
done; assert false
with Exit -> (* result *) end


In these cases, a tail-recursive function is more succint.