From 0191fb3768820da9287c3bd401593664f40aec7b Mon Sep 17 00:00:00 2001
From: Claudio Sacerdoti Coen <claudio.sacerdoticoen@unibo.it>
Date: Tue, 3 Feb 2004 14:07:43 +0000
Subject: [PATCH] Meta vs same Meta now tries unification when convertibility
 of the two substitutions fails.

---
 helm/ocaml/cic_unification/cicUnification.ml | 29 ++++++++++++++------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/helm/ocaml/cic_unification/cicUnification.ml b/helm/ocaml/cic_unification/cicUnification.ml
index c23aada3d..70c7aa9cb 100644
--- a/helm/ocaml/cic_unification/cicUnification.ml
+++ b/helm/ocaml/cic_unification/cicUnification.ml
@@ -56,25 +56,34 @@ let rec fo_unif_subst subst context metasenv t1 t2 =
  let module S = CicSubstitution in
   match (t1, t2) with
      (C.Meta (n,ln), C.Meta (m,lm)) when n=m ->
-       let ok =
+       let ok,subst,metasenv =
         List.fold_left2
-         (fun b t1 t2 ->
-           b &&
+         (fun (b,subst,metasenv) t1 t2 ->
+           if b then true,subst,metasenv else
             match t1,t2 with
                None,_
-             | _,None -> true
+             | _,None -> true,subst,metasenv
              | Some t1', Some t2' ->
                 (* First possibility:  restriction    *)
                 (* Second possibility: unification    *)
                 (* Third possibility:  convertibility *)
-                R.are_convertible subst context t1' t2'
-         ) true ln lm
+                if R.are_convertible subst context t1' t2' then
+                 true,subst,metasenv
+                else
+                 (try
+                   let subst,metasenv =
+                    fo_unif_subst subst context metasenv t1' t2'
+                   in
+                    true,subst,metasenv
+                 with
+                  Not_found -> false,subst,metasenv)
+         ) (true,subst,metasenv) ln lm
        in
         if ok then
           subst,metasenv
         else
           raise (UnificationFailure (sprintf
-            "Error trying to unify %s with %s: the algorithm only tried to check convertibility of the two substitutions"
+            "Error trying to unify %s with %s: the algorithm tried to check whether the two substitutions are convertible; if they are not, it tried to unify the two substitutions. No restriction was attempted."
             (CicPp.ppterm t1) (CicPp.ppterm t2)))
    | (C.Meta (n,l), C.Meta (m,_)) when n>m ->
        fo_unif_subst subst context metasenv t2 t1
@@ -97,13 +106,17 @@ let rec fo_unif_subst subst context metasenv t1 t2 =
             type_of_aux' metasenv' subst'' context t
           in
            fo_unif_subst subst'' context metasenv' (S.lift_meta l meta_type) tyt
-        with CicTypeChecker.SortExpectedMetaFound _ ->
+        with _ ->
           (* TODO huge hack!!!!
            * we keep on unifying/refining in the hope that the problem will be
            * eventually solved. In the meantime we're breaking a big invariant:
            * the terms that we are unifying are no longer well typed in the
            * current context (in the worst case we could even diverge)
            *)
+(*
+prerr_endline "********* FROM NOW ON EVERY REASONABLE INVARIANT IS BROKEN.";
+prerr_endline "********* PROCEED AT YOUR OWN RISK. AND GOOD LUCK." ;
+*)
           (subst'', metasenv'))
    | (C.Var (uri1,exp_named_subst1),C.Var (uri2,exp_named_subst2))
    | (C.Const (uri1,exp_named_subst1),C.Const (uri2,exp_named_subst2)) ->
-- 
2.39.2