From 81ea97cc0dba73a41e38c97d768c78b68126b0bc Mon Sep 17 00:00:00 2001
From: Enrico Tassi <enrico.tassi@inria.fr>
Date: Wed, 14 May 2008 16:27:16 +0000
Subject: [PATCH] partial implementation of reduction up to a given height

---
 .../components/ng_kernel/nCicReduction.ml     | 55 ++++++++++++-------
 1 file changed, 35 insertions(+), 20 deletions(-)

diff --git a/helm/software/components/ng_kernel/nCicReduction.ml b/helm/software/components/ng_kernel/nCicReduction.ml
index 32c553367..9cae8d409 100644
--- a/helm/software/components/ng_kernel/nCicReduction.ml
+++ b/helm/software/components/ng_kernel/nCicReduction.ml
@@ -520,7 +520,7 @@ let are_convertible whd ?(subst=[])  =
               (NCicSubstitution.lift s1 t1) 
               (NCicSubstitution.lift s2 t2))  
             l1 l2
-          with Invalid_argument _ -> false)
+          with Invalid_argument _ -> assert false)
 
        | C.Meta (n1,l1), _ ->
           (try 
@@ -553,26 +553,41 @@ let are_convertible whd ?(subst=[])  =
    if aux2 test_equality_only t1 t2 then 
      true
    else
-     let rec convert_machines = function
-      | [] -> true
-      | ((k1,env1,h1,s1),(k2,env2,h2,s2))::tl ->
-          aux2 test_equality_only
-           (R.unwind (k1,env1,h1,[])) (R.unwind (k2,env2,h2,[])) &&
-          let problems =
-           let red_stack =
-             List.map
-               (fun si-> R.reduce ~delta:0 ~subst context(RS.from_stack si))
-           in
-           try Some (List.combine (red_stack s1) (red_stack s2) @ tl)
-           with Invalid_argument _ -> None
-          in
-          match problems with
-           | None -> false
-           | Some problems -> convert_machines problems
+     let height_of = function
+      | NCic.Const (NReference.Ref (h,_,_)) -> h
+      | NCic.Appl (NCic.Const (NReference.Ref (h,_,_))::_) -> h
+      | _ -> 0
      in
-      convert_machines 
-       [R.reduce ~delta:0 ~subst context (0,[],t1,[]),
-        R.reduce ~delta:0 ~subst context (0,[],t2,[])]
+     let min_delta (k1,env1,t1,s1) (k2,env2,t2,s2) = 
+       let h1 = height_of t1 and h2 = height_of t2 in
+       if h1 > h2 then
+         R.reduce ~delta:(h2+1) ~subst context (k1,env1,t1,s1), 
+         (k2,env2,t2,s2), h2+1
+       else if h1 < h2 then
+         (k1,env1,t1,s1), 
+         R.reduce ~delta:(h1+1) ~subst context (k2,env2,t2,s2),
+         h1+1
+       else
+         R.reduce ~delta:(max 0 (h1-1)) ~subst context (k1,env1,t1,s1),
+         R.reduce ~delta:(max 0 (h1-1)) ~subst context (k2,env2,t2,s2),
+         (max 0 (h1-1))
+     in
+     let rec convert_machines ((k1,e1,t1,s1 as m1),(k2,e2,t2,s2 as m2),delta) todo =
+       (aux2 test_equality_only
+         (R.unwind (k1,e1,t1,[])) (R.unwind (k2,e2,t2,[])) &&
+       try
+         match List.combine s1 s2 @ todo with
+         | [] -> true
+         | (t1,t2) :: todo -> 
+             let t1 = RS.from_stack t1 and t2 = RS.from_stack t2 in
+             convert_machines (min_delta t1 t2) todo
+       with Invalid_argument _ -> false) || 
+       (delta > 0 &&
+         let delta = delta - 1 in 
+         let red = R.reduce ~delta ~subst context in
+         convert_machines (red m1,red m2,delta) todo)
+     in
+     convert_machines (min_delta (0,[],t1,[]) (0,[],t2,[])) []
  in
   aux false 
 ;;
-- 
2.39.2