Question

Suppose I have a function list_fun : int_list -> string list and in that function I use a StringSet that I define as module StringSet = Set.Make(String). I try to have the function return Set.elements s and get a string list but instead I get a StringSet.elt list which is supposed to be the same thing, as the StringSet‘s type t = string

How do you make OCaml understand that these types are identically defined? I have several cases where I have come across this issue as I have started using the OCaml standard library functions.

Answer 1

OCaml already knows that they are identically defined – unless you’re doing something strange to hide the types behind an abstraction, it will treat a StringSet.elt list and string list as the same type.