added explicit memoization cached interface and type

Signed-off-by: Rudi Horn <dyn-git@rudi-horn.de>

src/build_system.ml

@@ -398,7 +398,7 @@ type t =
   ; (* Package files are part of *)
     packages : Package.Name.t Path.Table.t
   (* memoized functions *)
-  ; cache_static_deps : (Memoization_cached.Id.t * Static_deps.t Fiber.t) -> (Static_deps.t Fiber.t)
+  ; cache_static_deps : Static_deps.t Memoization_cached.t
   ; prepare_rule_def : (Internal_rule.t * (unit, Action.t) Build.t, Action.t * Deps.t) Fdecl.comp
   ; build_rule_def : (Internal_rule.t * (unit, Action.t) Build.t, Action.t * Deps.t) Fdecl.comp
   ; build_file_def : (Path.t * Loc.t option, unit) Fdecl.comp

src/memoization_cached.ml

@@ -4,6 +4,8 @@ open Memoization_specs
 
 module Id = Id.Make ()
 
+type 'a t = Id.t * 'a Fiber.t -> 'a Fiber.t
+
 let id_input_spec =
   let ser x = Id.to_int x |> string_of_int in
   let ne x y = x <> y in

src/memoization_cached.mli

@@ -0,0 +1,5 @@
+type 'a t
+
+val cached : unit -> 'a t
+
+val cache : 'a t -> 'a Fiber.t -> 'a Fiber.t