@@ -7,10 +7,10 @@ (defstruct cd :title :artist :rating :ripped) ; pass db (not mutable data) -(defn add-records [db & cd] (concat db cd)) +(defn add-records [db & cd] (into db cd)) (defn init-db [] - (add-records '() + (add-records #{} (struct cd "Roses" "Kathy Mattea" 7 true) (struct cd "Fly" "Dixie Chicks" 8 true) (struct cd "Home" "Dixie Chicks" 9 true))) @@ -18,8 +18,8 @@ ; use two doseqs (String/format not as flexible as CL format) ; better way than wrapping cd in (seq cd)? (defn dump-db [db] - (doseq cd db - (doseq [key value] (seq cd) + (doseq rec db + (doseq [key value] rec (print (format "%10s: %s\n" (name key) value))) (println))) @@ -77,21 +77,26 @@ ; (filter (cddb/artist-selector "Dixie Chicks") (cddb/init-db)) ; more general (but allows "bad" keys to be specified) +; simpler with 'every but written this way for demo purposes (defn where [criteria] - (fn [cd] + (fn [m] (loop [criteria criteria] (let [[k,v] (first criteria)] (or (not k) - (and (= (k cd) v) (recur (rest criteria)))))))) - -; in Clojure it is idiomatic for the functional argument to come first -(defn update [criteria db updates] - (map - (fn [cd] - (if (criteria cd) - (merge cd updates) - cd)) - db)) + (and (= (k m) v) (recur (rest criteria)))))))) + +; use a built in seq function +(defn simpler-where [criteria] + (fn [m] + (every? (fn [[k v]] (= (k m) v)) criteria))) + +; RH recommends putting db first here for alter/commute purposes +; into lets us generalize for different collections +(defn update [db criteria updates] + (into (empty db) + (map (fn [m] + (if (criteria m) (merge m updates) m)) + db))) (defmacro backwards [expr] (reverse expr)) pcl/chap_03/chap_03.clj fd6d831ba41d46a82bd3804987dd545d4442895d Stuart Halloway stu@thinkrelevance.com http://github.com/stuarthalloway/practical-cl-clojure/commit/2423320922c368bf7ab1f732aeed7ae06580b956 2423320922c368bf7ab1f732aeed7ae06580b956

2008-09-17T10:11:23-07:00

updates per Rich Hickey's suggestions f45737355db031cb73185ee11e62f18fea150e39 Stuart Halloway stu@thinkrelevance.com