OCaml compiler library : Asttypes

`sig
type constant =
Const_int of int
| Const_char of char
| Const_string of string * Location.t * string option
| Const_float of string
| Const_int32 of int32
| Const_int64 of int64
| Const_nativeint of nativeint
type rec_flag = Nonrecursive | Recursive
type direction_flag = Upto | Downto
type private_flag = Private | Public
type mutable_flag = Immutable | Mutable
type virtual_flag = Virtual | Concrete
type override_flag = Override | Fresh
type closed_flag = Closed | Open
type label = string
type arg_label = Nolabel | Labelled of string | Optional of string
type 'a loc = 'a Location.loc = { txt : 'a; loc : Location.t; }
type variance = Covariant | Contravariant | NoVariance
type injectivity = Injective | NoInjectivity
end`