Leveraging GADTs to provide a better Dyn API.

9 files changed, 57 insertions, 31 deletions

diff --git a/lib/cSig.mli b/lib/cSig.mli
index 4463e8d9c..796e58cbf 100644
--- a/lib/cSig.mli
+++ b/lib/cSig.mli
@@ -14,6 +14,8 @@ type ('a, 'b) union = Inl of 'a | Inr of 'b
 type 'a until = Stop of 'a | Cont of 'a
 (** Used for browsable-until structures. *)
 
+type (_, _) eq = Refl : ('a, 'a) eq
+
 module type SetS =
 sig
     type elt
diff --git a/lib/dyn.ml b/lib/dyn.ml
index 60167ef1b..0571f3b5d 100644
--- a/lib/dyn.ml
+++ b/lib/dyn.ml
@@ -11,12 +11,12 @@ open Pp
 
 module type S =
 sig
-type t
+type 'a tag
+type t = Dyn : 'a tag * 'a -> t
 
-val create : string -> ('a -> t) * (t -> 'a)
-val tag : t -> string
-val has_tag : t -> string -> bool
-val pointer_equal : t -> t -> bool
+val create : string -> 'a tag
+val eq : 'a tag -> 'b tag -> ('a, 'b) CSig.eq option
+val repr : 'a tag -> string
 val dump : unit -> (int * string) list
 end
 
@@ -24,7 +24,9 @@ module Make(M : CSig.EmptyS) =
 struct
 (* Dynamics, programmed with DANGER !!! *)
 
-type t = int * Obj.t
+type 'a tag = int
+
+type t = Dyn : 'a tag * 'a -> t
 
 let dyntab = ref (Int.Map.empty : string Int.Map.t)
 (** Instead of working with tags as strings, which are costly, we use their
@@ -41,25 +43,16 @@ let create (s : string) =
       anomaly ~label:"Dyn.create" msg
   in
   let () = dyntab := Int.Map.add hash s !dyntab in
-  let infun v = (hash, Obj.repr v) in
-  let outfun (nh, rv) =
-    if Int.equal hash nh then Obj.magic rv
-    else
-      anomaly (str "dyn_out: expected " ++ str s)
-  in
-  (infun, outfun)
+  hash
 
-let has_tag (s, _) tag =
-  let hash = Hashtbl.hash (tag : string) in
-  Int.equal s hash
+let eq : 'a 'b. 'a tag -> 'b tag -> ('a, 'b) CSig.eq option =
+  fun h1 h2 -> if Int.equal h1 h2 then Some (Obj.magic CSig.Refl) else None
 
-let tag (s,_) =
+let repr s =
   try Int.Map.find s !dyntab
   with Not_found ->
     anomaly (str "Unknown dynamic tag " ++ int s)
 
-let pointer_equal (t1,o1) (t2,o2) = t1 = t2 && o1 == o2
-
 let dump () = Int.Map.bindings !dyntab
 
 end
\ No newline at end of file
diff --git a/lib/dyn.mli b/lib/dyn.mli
index 55c4f0ce8..28587859e 100644
--- a/lib/dyn.mli
+++ b/lib/dyn.mli
@@ -10,12 +10,12 @@
 
 module type S =
 sig
-type t
+type 'a tag
+type t = Dyn : 'a tag * 'a -> t
 
-val create : string -> ('a -> t) * (t -> 'a)
-val tag : t -> string
-val has_tag : t -> string -> bool
-val pointer_equal : t -> t -> bool
+val create : string -> 'a tag
+val eq : 'a tag -> 'b tag -> ('a, 'b) CSig.eq option
+val repr : 'a tag -> string
 val dump : unit -> (int * string) list
 end
 
diff --git a/lib/util.ml b/lib/util.ml
index a20dba0fc..b67539918 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -124,6 +124,7 @@ let delayed_force f = f ()
 
 type ('a, 'b) union = ('a, 'b) CSig.union = Inl of 'a | Inr of 'b
 type 'a until = 'a CSig.until = Stop of 'a | Cont of 'a
+type ('a, 'b) eq = ('a, 'b) CSig.eq = Refl : ('a, 'a) eq
 
 let map_union f g = function
   | Inl a -> Inl (f a)
diff --git a/lib/util.mli b/lib/util.mli
index 1dc405fcb..0ce6cc660 100644
--- a/lib/util.mli
+++ b/lib/util.mli
@@ -111,5 +111,7 @@ val map_union : ('a -> 'c) -> ('b -> 'd) -> ('a, 'b) union -> ('c, 'd) union
 type 'a until = 'a CSig.until = Stop of 'a | Cont of 'a
 (** Used for browsable-until structures. *)
 
+type ('a, 'b) eq = ('a, 'b) CSig.eq = Refl : ('a, 'a) eq
+
 val open_utf8_file_in : string -> in_channel
 (** Open an utf-8 encoded file and skip the byte-order mark if any. *)
diff --git a/library/declaremods.ml b/library/declaremods.ml
index 7f607a51c..d8c5ab5e7 100644
--- a/library/declaremods.ml
+++ b/library/declaremods.ml
@@ -371,7 +371,7 @@ let rec replace_module_object idl mp0 objs0 mp1 objs1 =
   match idl, objs0 with
   | _,[] -> []
   | id::idl,(id',obj)::tail when Id.equal id id' ->
-    assert (object_has_tag obj "MODULE");
+    assert (String.equal (object_tag obj) "MODULE");
     let mp_id = MPdot(mp0, Label.of_id id) in
     let objs = match idl with
       | [] -> Lib.subst_objects (map_mp mp1 mp_id empty_delta_resolver) objs1
diff --git a/library/libobject.ml b/library/libobject.ml
index c63875907..f0d281a2d 100644
--- a/library/libobject.ml
+++ b/library/libobject.ml
@@ -8,6 +8,7 @@
 
 open Libnames
 open Pp
+open Util
 
 module Dyn = Dyn.Make(struct end)
 
@@ -72,15 +73,25 @@ type dynamic_object_declaration = {
   dyn_discharge_function : object_name * obj -> obj option;
   dyn_rebuild_function : obj -> obj }
 
-let object_tag = Dyn.tag
-let object_has_tag = Dyn.has_tag
+let object_tag (Dyn.Dyn (t, _)) = Dyn.repr t
 
 let cache_tab =
   (Hashtbl.create 17 : (string,dynamic_object_declaration) Hashtbl.t)
 
+let make_dyn (type a) (tag : a Dyn.tag) =
+  let infun x = Dyn.Dyn (tag, x) in
+  let outfun : (Dyn.t -> a) = fun dyn ->
+    let Dyn.Dyn (t, x) = dyn in
+    match Dyn.eq t tag with
+    | None -> assert false
+    | Some Refl -> x
+  in
+  (infun, outfun)
+
 let declare_object_full odecl =
   let na = odecl.object_name in
-  let (infun,outfun) = Dyn.create na in
+  let tag = Dyn.create na in
+  let (infun, outfun) = make_dyn tag in
   let cacher (oname,lobj) = odecl.cache_function (oname,outfun lobj)
   and loader i (oname,lobj) = odecl.load_function i (oname,outfun lobj)
   and opener i (oname,lobj) = odecl.open_function i (oname,outfun lobj)
diff --git a/library/libobject.mli b/library/libobject.mli
index e49f3fd5c..12b1a558f 100644
--- a/library/libobject.mli
+++ b/library/libobject.mli
@@ -99,7 +99,6 @@ val declare_object :
   'a object_declaration -> ('a -> obj)
 
 val object_tag : obj -> string
-val object_has_tag : obj -> string -> bool
 
 val cache_object : object_name * obj -> unit
 val load_object : int -> object_name * obj -> unit
diff --git a/library/summary.ml b/library/summary.ml
index 6ef4e131c..a922e155d 100644
--- a/library/summary.ml
+++ b/library/summary.ml
@@ -22,8 +22,19 @@ let summaries = ref Int.Map.empty
 
 let mangle id = id ^ "-SUMMARY"
 
+let make_dyn (type a) (tag : a Dyn.tag) =
+  let infun x = Dyn.Dyn (tag, x) in
+  let outfun : (Dyn.t -> a) = fun dyn ->
+    let Dyn.Dyn (t, x) = dyn in
+    match Dyn.eq t tag with
+    | None -> assert false
+    | Some Refl -> x
+  in
+  (infun, outfun)
+
 let internal_declare_summary hash sumname sdecl =
-  let (infun, outfun) = Dyn.create (mangle sumname) in
+  let tag = Dyn.create (mangle sumname) in
+  let (infun, outfun) = make_dyn tag in
   let dyn_freeze b = infun (sdecl.freeze_function b)
   and dyn_unfreeze sum = sdecl.unfreeze_function (outfun sum)
   and dyn_init = sdecl.init_function in
@@ -166,8 +177,15 @@ let project_summary { summaries; ml_module } ?(complement=false) ids =
   List.filter (fun (id, _) -> List.mem id ids) summaries
 
 let pointer_equal l1 l2 =
+  let ptr_equal d1 d2 =
+    let Dyn.Dyn (t1, x1) = d1 in
+    let Dyn.Dyn (t2, x2) = d2 in
+    match Dyn.eq t1 t2 with
+    | None -> false
+    | Some Refl -> x1 == x2
+    in
   CList.for_all2eq
-    (fun (id1,v1) (id2,v2) -> id1 = id2 && Dyn.pointer_equal v1 v2) l1 l2
+    (fun (id1,v1) (id2,v2) -> id1 = id2 && ptr_equal v1 v2) l1 l2
 
 (** All-in-one reference declaration + registration *)