Snippet to toggle requiring/not requiring ;; in utop

toggle_semi.ml

(* Put this in ~/.ocamlinit to be able to toggle requiring ;; on and off *)

let toggle_semi =
  let original = !UTop.parse_toplevel_phrase in
  let no_semi str eos_is_error = original (str ^ ";;") eos_is_error in
  let semi = ref true in
  fun () ->
    UTop.parse_toplevel_phrase := if !semi then no_semi else original;
    semi := not !semi
;;
(* Include this line to not require ;; by default *)
toggle_semi ();;

The method and idea is originally from ocaml-community/utop#131

We can then hook up a single key e.g. F5 to use your toggle function!

#require "lambda-term"

let () =
  LTerm_read_line.bind
    [{control = false; meta = false; shift = false; code = F5}]
    [LTerm_read_line.Edit (Custom toggle_semi)]

Ah, not bad!