Declarations.mli refactoring: module_type_body = module_body

 After this commit, module_type_body is a particular case of module_type.
 For a [module_type_body], the implementation field [mod_expr] is
 supposed to be always [Abstract]. This is verified by coqchk, even
 if this isn't so crucial, since [mod_expr] is never read in the case
 of a module type.

 Concretely, this amounts to the following rewrite on field names
 for module_type_body:
  - typ_expr --> mod_type
  - typ_expr_alg --> mod_type_alg
  - typ_* --> mod_*
 and adding two new fields to mtb:
  - mod_expr (always containing Abstract)
  - mod_retroknowledge (always containing [])

 This refactoring should be completely transparent for the user.

 Pros: code sharing, for instance subst_modtype = subst_module.
 Cons: a runtime invariant (mod_expr = Abstract) which isn't
 enforced by typing. I tried a polymorphic typing of mod_expr,
 to share field names while not having mtb = mb, but the OCaml
 typechecker isn't clever enough with polymorphic mutual fixpoints,
 and reject code sharing (e.g. between subst_modtype and subst_module).
 In the future (with ocaml>=4), some GADT could maybe help here,
 but for now the current solution seems good enough.

1 files changed, 12 insertions, 14 deletions

diff --git a/checker/mod_checking.ml b/checker/mod_checking.ml
index 9e61d3491..998e23c6e 100644
--- a/checker/mod_checking.ml
+++ b/checker/mod_checking.ml
@@ -64,6 +64,15 @@ let lookup_module mp env =
   with Not_found ->
     failwith ("Unknown module: "^string_of_mp mp)
 
+let mk_mtb mp sign delta =
+  { mod_mp = mp;
+    mod_expr = Abstract;
+    mod_type = sign;
+    mod_type_alg = None;
+    mod_constraints = Univ.Constraint.empty;
+    mod_delta = delta;
+    mod_retroknowledge = []; }
+
 let rec check_module env mp mb =
   let (_:module_signature) =
     check_signature env mb.mod_type mb.mod_mp mb.mod_delta
@@ -76,25 +85,14 @@ let rec check_module env mp mb =
   match optsign with
   |None -> ()
   |Some sign ->
-    let mtb1 =
-      {typ_mp=mp;
-       typ_expr=sign;
-       typ_expr_alg=None;
-       typ_constraints=Univ.Constraint.empty;
-       typ_delta = mb.mod_delta;}
-    and mtb2 =
-      {typ_mp=mp;
-       typ_expr=mb.mod_type;
-       typ_expr_alg=None;
-       typ_constraints=Univ.Constraint.empty;
-       typ_delta = mb.mod_delta;}
-    in
+    let mtb1 = mk_mtb mp sign mb.mod_delta
+    and mtb2 = mk_mtb mp mb.mod_type mb.mod_delta in
     let env = add_module_type mp mtb1 env in
     Subtyping.check_subtypes env mtb1 mtb2
 
 and check_module_type env mty =
   let (_:module_signature) =
-    check_signature env mty.typ_expr mty.typ_mp mty.typ_delta in
+    check_signature env mty.mod_type mty.mod_mp mty.mod_delta in
   ()
 
 and check_structure_field env mp lab res = function