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, 4 insertions, 3 deletions

diff --git a/checker/values.ml b/checker/values.ml
index 0ac8bf78c..5c4876e59 100644
--- a/checker/values.ml
+++ b/checker/values.ml
@@ -13,7 +13,7 @@
 To ensure this file is up-to-date, 'make' now compares the md5 of cic.mli
 with a copy we maintain here:
 
-MD5 27f35ee65fef280d5a7a80bb11b31837 checker/cic.mli
+MD5 f4d390282966a3fbd22a9e384046d231 checker/cic.mli
 
 *)
 
@@ -296,15 +296,16 @@ and v_mexpr =
   [|[|v_mae|];                     (* NoFunctor *)
     [|v_uid;v_modtype;v_mexpr|]|]) (* MoreFunctor *)
 and v_impl =
-  Sum ("module_impl",2,
+  Sum ("module_impl",2, (* Abstract, FullStruct *)
   [|[|v_mexpr|];  (* Algebraic *)
     [|v_sign|]|])  (* Struct *)
+and v_noimpl = v_enum "no_impl" 1 (* Abstract is mandatory for mtb *)
 and v_module =
   Tuple ("module_body",
          [|v_mp;v_impl;v_sign;Opt v_mexpr;v_cstrs;v_resolver;Any|])
 and v_modtype =
   Tuple ("module_type_body",
-         [|v_mp;v_sign;Opt v_mexpr;v_cstrs;v_resolver|])
+         [|v_mp;v_noimpl;v_sign;Opt v_mexpr;v_cstrs;v_resolver;Any|])
 
 (** kernel/safe_typing *)