Example (on a 32-bit machine): Objective Caml version 3.10.2+rc1 # let x = Obj.repr 1;; val x : Obj.t = <abstr> # let y = Obj.repr 1.0;; val y : Obj.t = <abstr> # [| x; y |];; - : Obj.t array = [|<abstr>; <abstr>|] # [| y; x |];; Bus error