type 'a t
= ('a, Core.immutable) any
include sig ... end
val t_of_sexp : (Base.Sexp.t ‑> 'a) ‑> Base.Sexp.t ‑> 'a t
val sexp_of_t : ('a ‑> Base.Sexp.t) ‑> 'a t ‑> Base.Sexp.t