make f is a make function that will give f a safely constructed t.

Typically this is used to extend the constructor for t with new optional arguments.

E.g., we can construct a configuration that includes a t alongside a more specific field like so:

  type extended_config = {
    new_field: string;
    common: t;
  }

  let make : (new_field:string -> unit -> extended_config) make =
    Env.make (fun common ~new_field () -> { new_field; common })

  let _example : extended_config =
    make ~new_field:"foo" ~url_traces:"foo/bar" ~debug:true ()

As a special case, we can get the simple constructor function for t with Env.make (fun common () -> common)