List.nth not guarded by try ... with. Fixed.

diff --git a/helm/ocaml/cic_unification/cicMetaSubst.ml b/helm/ocaml/cic_unification/cicMetaSubst.ml
index e7b0e3661387d3b986a292858962532f9c4588a5..7cf16ee53403f1d908c20984a3834d42f445e514 100644 (file)
--- a/helm/ocaml/cic_unification/cicMetaSubst.ml
+++ b/helm/ocaml/cic_unification/cicMetaSubst.ml
@@ -504,14 +504,19 @@ let delift n subst context metasenv l t =
                     (*CSC: deliftato la regola per il LetIn                 *)
                     (*CSC: FALSO! La regola per il LetIn non lo fa          *)
          else
-          (match List.nth context (m-k-1) with
-            Some (_,C.Def (t,_)) ->
-             (*CSC: Hmmm. This bit of reduction is not in the spirit of    *)
-             (*CSC: first order unification. Does it help or does it harm? *)
-             deliftaux k (S.lift m t)
-          | Some (_,C.Decl t) ->
-             C.Rel ((position (m-k) l) + k)
-          | None -> raise (MetaSubstFailure "RelToHiddenHypothesis"))
+          (try
+            match List.nth context (m-k-1) with
+               Some (_,C.Def (t,_)) ->
+                (*CSC: Hmmm. This bit of reduction is not in the spirit of    *)
+                (*CSC: first order unification. Does it help or does it harm? *)
+                deliftaux k (S.lift m t)
+             | Some (_,C.Decl t) ->
+                C.Rel ((position (m-k) l) + k)
+             | None -> raise (MetaSubstFailure "RelToHiddenHypothesis")
+           with
+            Failure _ ->
+             raise (MetaSubstFailure "Unbound variable found in deliftaux")
+          )
      | C.Var (uri,exp_named_subst) ->
         let exp_named_subst' =
          List.map (function (uri,t) -> uri,deliftaux k t) exp_named_subst