From: Claudio Sacerdoti Coen <claudio.sacerdoticoen@unibo.it>
Date: Thu, 3 Nov 2005 15:07:55 +0000 (+0000)
Subject: Semantic change: I always consider a type with no constructors as an empty
X-Git-Tag: V_0_7_2_3~144
X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=commitdiff_plain;h=f32d668005b27b2eb8cc984a5dd57506b2d1f7e7;p=helm.git

Semantic change: I always consider a type with no constructors as an empty
type even if it is mutually recursive with non-empty types. I think that
this should be a sound generalization.

Note: Coq assumes a type to be empty iff it is not mutually recursive with
any other inductive type.
---

diff --git a/helm/ocaml/cic_proof_checking/cicTypeChecker.ml b/helm/ocaml/cic_proof_checking/cicTypeChecker.ml
index 611585400..af98ff0ef 100644
--- a/helm/ocaml/cic_proof_checking/cicTypeChecker.ml
+++ b/helm/ocaml/cic_proof_checking/cicTypeChecker.ml
@@ -1308,7 +1308,7 @@ and check_allowed_sort_elimination ~subst ~metasenv ~logger context uri i
            let itl_len = List.length itl in
            let (name,_,ty,cl) = List.nth itl i in
            let cl_len = List.length cl in
-            if (itl_len = 1 && cl_len <= 1) then
+            if (cl_len = 0 || (itl_len = 1 && cl_len = 1)) then
              let non_informative,ugraph =
               if cl_len = 0 then true,ugraph
               else
@@ -1319,12 +1319,7 @@ and check_allowed_sort_elimination ~subst ~metasenv ~logger context uri i
                  definition? *)
               non_informative, ugraph
             else
-             let is_empty =
-              List.fold_left
-               (fun b (_,_,_,cl) -> b && List.length cl = 0) true itl
-             in
-              (* is it a block of mutual inductive empty definitions? *)
-              is_empty,ugraph
+              false,ugraph
          | _ ->
              raise (TypeCheckerFailure 
 		     (lazy ("Unknown mutual inductive definition:" ^
diff --git a/helm/ocaml/cic_proof_checking/doc/inductive.txt b/helm/ocaml/cic_proof_checking/doc/inductive.txt
index 4cc9cade6..f2e49d398 100644
--- a/helm/ocaml/cic_proof_checking/doc/inductive.txt
+++ b/helm/ocaml/cic_proof_checking/doc/inductive.txt
@@ -36,5 +36,6 @@ Legenda:
   non-informative : Constructor arguments are in Prop only
   small : Constructor arguments are not in Type and SetP and CProp
   unit : Non (mutually) recursive /\ only one constructor /\ non-informative
-  empty : no contructors and (in Coq) non mutually recursive
-            
+  empty : in Coq:    no constructors and non mutually recursive
+          in Matita: no constructors (but eventually mutually recursive
+                     with non-empty types)