Functor Tuple.Hashable

module Hashable: 
functor (S1 : Hashable_sexpable) -> 
functor (S2 : Hashable_sexpable) -> Hashable_sexpable  with type t := Make (S1) (S2).t

The difference between Hashable and Hashable_t functors is that the former's result type doesn't contain type t and the latter does. Therefore, Hashable can't be used to combine two pairs into 4-tuple. but Hashable_t can. On the other hand result of Hashable_t cannot be combined with Comparable.

example: module Four_ints = Tuple.Hashable_t (Tuple.Hashable_t (Int)(Int)) (Tuple.Hashable_t (Int)(Int))

If instead we used Hashable compiler would complain that the input to outer functor doesn't have type t.

On the other hand: module Foo = struct type t = String.t * Int.t include Tuple.Comparable (String.t) (Int) include Tuple.Hashable (String.t) (Int) end

If we used Hashable_t above, compiler would compile that we have two types t defined.

Unfortunately, it is not possible to define just one functor that could be used in both cases.

type t 

include Hashable.S

val t_of_sexp : Sexplib.Sexp.t -> t

val sexp_of_t : t -> Sexplib.Sexp.t