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updates per Rich Hickey's suggestions

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stuarthalloway committed Sep 17, 2008
1 parent fd6d831 commit 2423320922c368bf7ab1f732aeed7ae06580b956
Showing with 20 additions and 15 deletions.
  1. +20 −15 pcl/chap_03/chap_03.clj
@@ -7,19 +7,19 @@
(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)))

; 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))

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