Added cache to lpo implementation.

The current cache is based on imperative lists.
Can it be improved with smarter data structures (e.g. HashTables?)

diff --git a/matita/components/ng_paramodulation/orderings.ml b/matita/components/ng_paramodulation/orderings.ml
index b457832453dd5582b5d44c95c9c292fb68578ac0..bf033ec662d058ead724ec7195981eedceeffb8f 100644 (file)
--- a/matita/components/ng_paramodulation/orderings.ml
+++ b/matita/components/ng_paramodulation/orderings.ml
@@ -363,10 +363,16 @@ module LPO (B : Terms.Blob) = struct
   let compute_unit_clause_weight = compute_unit_clause_weight;;
   let compute_goal_weight = compute_goal_weight;;
 
+  (*CSC: beware! Imperative cache! *)
+  let cache = ref [];;
+
   let rec lpo_le s t = 
     eq_foterm s t || lpo_lt s t 
   
   and lpo_lt s t =
+    try List.assoc (s,t) !cache
+    with
+    Not_found -> let res =
     match s,t with
       | _, Terms.Var _ -> false
       | Terms.Var i,_ ->
@@ -399,13 +405,18 @@ module LPO (B : Terms.Blob) = struct
                 compare_args tl1 tl2
             | _ -> assert false
            end
+   in
+    cache := ((s,t),res)::!cache; res
   ;;
 
   let lpo s t =
+    let res =
     if eq_foterm s t then XEQ
     else if lpo_lt s t then XLT
     else if lpo_lt t s then XGT
     else XINCOMPARABLE
+    in
+     cache := []; res
   ;;