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1 (ns mtg.frame)
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2
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3 ;; GENERALLY USEFUL FUNCTIONS
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4
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5 (defn assay "Takes x and a series of pred-value pairs. Returns a list of vals for which the corresponding preds are true of x." [x & pred-vals]
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6 (reduce #(if ((first %2) x) (conj %1 (second %2))) '() pred-vals)
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7 )
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8 (defn alter-val "Applies f to the current value associated with each key, associating each key with the value returned." [m f & keys]
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9 (map #(assoc m % (f (get m %))) keys))
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10
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11 (defn every-nth "Returns every nth member of coll. If n is not positive, returns an empty list." [n coll]
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12 (if (<= n 0) '()
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13 (take-while (comp not nil?) (map first (iterate #(nthnext % n) coll)))))
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14
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15
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16
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17
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18
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19 ;; FRAME MANIPULATION
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20
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21 (defn conj-key "Adds the xs to the seq associated with the given key." [map key & xs]
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22 (assoc map key (apply conj (get map key []) xs)))
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23
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24 (defn update "Takes a frame and a sequence of key-fn pairs. Applies f to the current value associated with key, updating the current value with the result. Frames generate and store a unique id for each call to update."
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25 [frame & kfs]
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26 (let [id (gensym "")
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27 keys (every-nth 2 kfs)
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28 fns (every-nth 2 (rest kfs))]
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29
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30 ((reduce comp (map (fn[k f](fn[m](conj-key m k (list id f)))) keys fns))
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31 (conj-key frame :*bindings* (map (fn [k f](list id k)) keys fns))
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32 )
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33 ))
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34
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35 (defn rollback "Undo the update with the given id." [frame id]
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36 (let [affected-keys
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37 (conj (map second (filter #(=(first %) id) (:*bindings* frame))) :*bindings*)]
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38 (reduce (fn[frame key]
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39 (alter-val (partial filter #(=(first %) id)) key)
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40 ) frame affected-keys)
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41 ))
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42
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43
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44 (defn get-fn "Keys in a frame store lists of modifiers. Produces the end result of applying all the modifiers in order." [frame key]
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45 (reduce #(%2) (constantly nil) (list (constantly 1)))
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46 )
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47
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48
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49 (def *frame* (atom {:*bindings* '()}))
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50
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