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+;;  Copyright (c) Jeffrey Straszheim. All rights reserved.  The use and
+;;  distribution terms for this software are covered by the Eclipse Public
+;;  License 1.0 (http://opensource.org/licenses/eclipse-1.0.php) which can
+;;  be found in the file epl-v10.html at the root of this distribution.  By
+;;  using this software in any fashion, you are agreeing to be bound by the
+;;  terms of this license.  You must not remove this notice, or any other,
+;;  from this software.
+;;
+;;  seminaive.clj
+;;
+;;  A Clojure implementation of Datalog -- Semi Naive Evaluation
+;;
+;;  straszheimjeffrey (gmail)
+;;  Created 5 March 2009
+
+
+(ns clojure.contrib.datalog.seminaive
+  (:use clojure.contrib.datalog.util
+        clojure.contrib.datalog.database
+        clojure.contrib.datalog.literals
+        clojure.contrib.datalog.rules
+        clojure.contrib.datalog.magic)
+  (:use [clojure.set :only (union intersection difference)])
+  (:use [clojure.contrib.seq-utils :only (indexed)])
+  (:require [clojure.contrib.graph :as graph]))
+
+
+;;;;  WORK IN PROGRESS !!!
+
+
+;;; Delta Rules
+
+(defn- compute-delta-rules*
+  "Perform the delta computation of a rule, where i-rules is the set
+   of intensional predicates."
+  [r i-preds]
+  (let [head (:head r)
+        head-negated (negated-literal head)
+        delta-head (delta-literal head)
+        body (:body r)
+        new-rules (loop [lit (first body)
+                        left []
+                        right (next body)
+                        results []]
+                   (if (nil? lit)
+                     results
+                     (let [new-results (if (i-preds lit)
+                                         (conj results
+                                               (assoc r :head delta-head
+                                                      :body (concat left
+                                                                    [(delta-literal lit)]
+                                                                    right
+                                                                    [head-negated])))
+                                         results)]
+                       (recur (first right)
+                              (conj left lit)
+                              (next right)
+                              new-results))))]
+    (if (empty? new-rules)
+      [(assoc r :head delta-head :body (conj (vec body) head-negated))]
+      new-rules)))
+
+
+(defn- compute-delta-rules
+  "Compute the delta rules of a rules set, where i-rules is the set of
+   intensional predicates."
+  [rs i-preds]
+  (mapcat #(compute-delta-rules* % i-preds) rs))
+
+
+
+;; End of file