rlm@10: ;;  Copyright (c) Jeffrey Straszheim. All rights reserved.  The use and
rlm@10: ;;  distribution terms for this software are covered by the Eclipse Public
rlm@10: ;;  License 1.0 (http://opensource.org/licenses/eclipse-1.0.php) which can
rlm@10: ;;  be found in the file epl-v10.html at the root of this distribution.  By
rlm@10: ;;  using this software in any fashion, you are agreeing to be bound by the
rlm@10: ;;  terms of this license.  You must not remove this notice, or any other,
rlm@10: ;;  from this software.
rlm@10: ;;
rlm@10: ;;  util.clj
rlm@10: ;;
rlm@10: ;;  A Clojure implementation of Datalog -- Utilities
rlm@10: ;;
rlm@10: ;;  straszheimjeffrey (gmail)
rlm@10: ;;  Created 3 Feburary 2009
rlm@10: 
rlm@10: 
rlm@10: (ns clojure.contrib.datalog.util
rlm@10:   (:use [clojure.contrib.seq :only (separate)]))
rlm@10: 
rlm@10: 
rlm@10: 
rlm@10: ;;; Bindings and logic vars.  A binding in a hash of logic vars to
rlm@10: ;;; bound values.  Logic vars are any symbol prefixed with a \?.
rlm@10: 
rlm@10: (defn is-var?
rlm@10:   "Is this a logic variable: e.g. a symbol prefixed with a ?"
rlm@10:   [sym]
rlm@10:   (when (symbol? sym)
rlm@10:     (let [name (name sym)]
rlm@10:       (and (= \? (first name))
rlm@10:            (not= \? (fnext name))))))
rlm@10: 
rlm@10: (defn is-query-var?
rlm@10:   "Is this a query variable: e.g. a symbol prefixed with ??"
rlm@10:   [sym]
rlm@10:   (when (symbol? sym)
rlm@10:     (let [name (name sym)]
rlm@10:       (and (= \? (first name))
rlm@10:            (= \? (fnext name))))))
rlm@10: 
rlm@10: (defn map-values
rlm@10:   "Like map, but works over the values of a hash map"
rlm@10:   [f hash]
rlm@10:   (let [key-vals (map (fn [[key val]] [key (f val)]) hash)]
rlm@10:     (if (seq key-vals)
rlm@10:       (apply conj (empty hash) key-vals)
rlm@10:       hash)))
rlm@10: 
rlm@10: (defn keys-to-vals
rlm@10:   "Given a map and a collection of keys, return the collection of vals"
rlm@10:   [m ks]
rlm@10:   (vals (select-keys m ks)))
rlm@10: 
rlm@10: (defn reverse-map
rlm@10:   "Reverse the keys/values of a map"
rlm@10:   [m]
rlm@10:   (into {} (map (fn [[k v]] [v k]) m)))
rlm@10: 
rlm@10: 
rlm@10: ;;; Preduce -- A parallel reduce over hashes
rlm@10:   
rlm@10: (defn preduce
rlm@10:   "Similar to merge-with, but the contents of each key are merged in
rlm@10:    parallel using f.
rlm@10: 
rlm@10:    f - a function of 2 arguments.
rlm@10:    data - a collection of hashes."
rlm@10:   [f data]
rlm@10:   (let [data-1 (map (fn [h] (map-values #(list %) h)) data)
rlm@10:         merged (doall (apply merge-with concat data-1))
rlm@10:         ; Groups w/ multiple elements are identified for parallel processing
rlm@10:         [complex simple] (separate (fn [[key vals]] (> (count vals) 1)) merged)
rlm@10:         fold-group (fn [[key vals]] {key (reduce f vals)})
rlm@10:         fix-single (fn [[key [val]]] [key val])]
rlm@10:     (apply merge (concat (pmap fold-group merged) (map fix-single simple)))))
rlm@10:   
rlm@10: 
rlm@10: ;;; Debuging and Tracing
rlm@10: 
rlm@10: (def *trace-datalog* nil)
rlm@10: 
rlm@10: (defmacro trace-datalog
rlm@10:   "If *test-datalog* is set to true, run the enclosed commands"
rlm@10:   [& body]
rlm@10:   `(when *trace-datalog*
rlm@10:      ~@body))
rlm@10: 
rlm@10:  	
rlm@10: ;; End of file