Duplicate (js_of_ocaml-compiler.Js_of_ocaml

val closure : 
  Code.program ->
  f:Code.Var.t ->
  params:Code.Var.t list ->
  cont:(int * Code.Var.t list) ->
  Code.program * Code.Var.t * Code.Var.t list * (int * Code.Var.t list)

Given a program and a closure f -- defined by its name, parameters, and its continuation --, return a program with a copy of f. Also returns the new name of f, and the similarly substituted parameter list and continuation.