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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
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