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ocamlvalue-restriction

Why this OCaml code does not subject to the value restriction

I don't understand that the function (my_path_mapper) doesn't subject to the value restriction.

# let rec my_map ~f l =
  match l with
    [] -> []
  | h::t -> f h::my_map f t;;
      val my_map : f:('a -> 'b) -> 'a list -> 'b list = <fun>
# let my_path_mapper =
  my_map ["/usr/sbin"; "/usr/bin"; "/sbin"; "/bin"; "/usr/games"; "/usr/local/games"];;
  val my_path_mapper : f:(string -> 'a) -> 'a list = <fun>

Please teach me Why ?

Solution

  • OCaml has a "relaxed value restriction." You can read about it here:

    Jacques Garrigue, Relaxing the Value Restriction

    Here is a previous discussion on StackOverflow:

    When does the relaxed value restriction kick in in OCaml?