Obj

`sig
type t
external repr : 'a -> Obj.t = "%identity"
external obj : Obj.t -> 'a = "%identity"
external magic : 'a -> 'b = "%identity"
external is_block : Obj.t -> bool = "caml_obj_is_block"
external is_int : Obj.t -> bool = "%obj_is_int"
external tag : Obj.t -> int = "caml_obj_tag"
external set_tag : Obj.t -> int -> unit = "caml_obj_set_tag"
external size : Obj.t -> int = "%obj_size"
external field : Obj.t -> int -> Obj.t = "%obj_field"
external set_field : Obj.t -> int -> Obj.t -> unit = "%obj_set_field"
val double_field : Obj.t -> int -> float
val set_double_field : Obj.t -> int -> float -> unit
external new_block : int -> int -> Obj.t = "caml_obj_block"
external dup : Obj.t -> Obj.t = "caml_obj_dup"
external truncate : Obj.t -> int -> unit = "caml_obj_truncate"
external add_offset : Obj.t -> Int32.t -> Obj.t = "caml_obj_add_offset"
val lazy_tag : int
val closure_tag : int
val object_tag : int
val infix_tag : int
val forward_tag : int
val no_scan_tag : int
val abstract_tag : int
val string_tag : int
val double_tag : int
val double_array_tag : int
val custom_tag : int
val final_tag : int
val int_tag : int
val out_of_heap_tag : int
val unaligned_tag : int
val extension_name : 'a -> string
val extension_id : 'a -> int
val extension_slot : 'a -> Obj.t
val marshal : Obj.t -> bytes
val unmarshal : bytes -> int -> Obj.t * int
end`