From edf85b925939cb13ca82a10873ced589164391da Mon Sep 17 00:00:00 2001
From: Pierre Letouzey
Date: Sat, 3 Jan 2015 18:50:53 +0100
Subject: 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.
---
 kernel/declarations.mli | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

(limited to 'kernel/declarations.mli')

diff --git a/kernel/declarations.mli b/kernel/declarations.mli
index 4f1672884f..2d5468ff18 100644
--- a/kernel/declarations.mli
+++ b/kernel/declarations.mli
@@ -251,17 +251,11 @@ and module_body =
     mod_delta : Mod_subst.delta_resolver;
     mod_retroknowledge : Retroknowledge.action list }
 
-(** A [module_type_body] is similar to a [module_body], with
-    no implementation and retroknowledge fields *)
-
-and module_type_body =
-  { typ_mp : module_path; (** path of the module type *)
-    typ_expr : module_signature; (** expanded type *)
-    (** algebraic expression, kept if it's relevant for extraction  *)
-    typ_expr_alg : module_expression option;
-    typ_constraints : Univ.constraints;
-    (** quotiented set of equivalent constants and inductive names *)
-    typ_delta : Mod_subst.delta_resolver}
+(** A [module_type_body] is just a [module_body] with no
+    implementation ([mod_expr] always [Abstract]) and also
+    an empty [mod_retroknowledge] *)
+
+and module_type_body = module_body
 
 (** Extra invariants :
 
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