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1 ;; Copyright (c) Jeffrey Straszheim. All rights reserved. The use and
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2 ;; distribution terms for this software are covered by the Eclipse Public
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3 ;; License 1.0 (http://opensource.org/licenses/eclipse-1.0.php) which can
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4 ;; be found in the file epl-v10.html at the root of this distribution. By
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5 ;; using this software in any fashion, you are agreeing to be bound by the
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6 ;; terms of this license. You must not remove this notice, or any other,
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7 ;; from this software.
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8 ;;
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9 ;; util.clj
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10 ;;
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11 ;; A Clojure implementation of Datalog -- Utilities
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12 ;;
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13 ;; straszheimjeffrey (gmail)
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14 ;; Created 3 Feburary 2009
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15
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16
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17 (ns clojure.contrib.datalog.util
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18 (:use [clojure.contrib.seq :only (separate)]))
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19
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20
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21
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22 ;;; Bindings and logic vars. A binding in a hash of logic vars to
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23 ;;; bound values. Logic vars are any symbol prefixed with a \?.
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24
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25 (defn is-var?
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26 "Is this a logic variable: e.g. a symbol prefixed with a ?"
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27 [sym]
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28 (when (symbol? sym)
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29 (let [name (name sym)]
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30 (and (= \? (first name))
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31 (not= \? (fnext name))))))
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32
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33 (defn is-query-var?
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34 "Is this a query variable: e.g. a symbol prefixed with ??"
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35 [sym]
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36 (when (symbol? sym)
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37 (let [name (name sym)]
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38 (and (= \? (first name))
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39 (= \? (fnext name))))))
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40
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41 (defn map-values
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42 "Like map, but works over the values of a hash map"
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43 [f hash]
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44 (let [key-vals (map (fn [[key val]] [key (f val)]) hash)]
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45 (if (seq key-vals)
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46 (apply conj (empty hash) key-vals)
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47 hash)))
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48
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49 (defn keys-to-vals
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50 "Given a map and a collection of keys, return the collection of vals"
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51 [m ks]
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52 (vals (select-keys m ks)))
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53
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54 (defn reverse-map
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55 "Reverse the keys/values of a map"
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56 [m]
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57 (into {} (map (fn [[k v]] [v k]) m)))
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58
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59
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60 ;;; Preduce -- A parallel reduce over hashes
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61
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62 (defn preduce
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63 "Similar to merge-with, but the contents of each key are merged in
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64 parallel using f.
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65
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66 f - a function of 2 arguments.
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67 data - a collection of hashes."
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68 [f data]
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69 (let [data-1 (map (fn [h] (map-values #(list %) h)) data)
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70 merged (doall (apply merge-with concat data-1))
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71 ; Groups w/ multiple elements are identified for parallel processing
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72 [complex simple] (separate (fn [[key vals]] (> (count vals) 1)) merged)
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73 fold-group (fn [[key vals]] {key (reduce f vals)})
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74 fix-single (fn [[key [val]]] [key val])]
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75 (apply merge (concat (pmap fold-group merged) (map fix-single simple)))))
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76
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77
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78 ;;; Debuging and Tracing
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79
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80 (def *trace-datalog* nil)
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81
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82 (defmacro trace-datalog
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83 "If *test-datalog* is set to true, run the enclosed commands"
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84 [& body]
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85 `(when *trace-datalog*
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86 ~@body))
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87
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88
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89 ;; End of file
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