SICP，延續傳球風格和Clojure的蹦牀

我與SICP一起工作，運動2.29-b讓我有機會在穿越手機和分支時獲得延續傳球風格。SICP，延續傳球風格和Clojure的蹦牀

爲了簡化故事，每個手機都有左右分支，它們由長度和數字權重或其他手機組成。這個問題要求找到手機的總重量。

第一相互遞歸解決方案之後，很簡單，我嘗試併成功實施了CPS'之一：

(defn total-weight-cps [mobile] 
    (letfn 
    [(branch-weight-cps 
     [branch kont] 
     (let [structure (branch-structure branch)] 
     (if (mobile? (branch-structure branch)) 
      (do (println "then " structure) (kont (traverse-mobile-cps structure identity))) 
      (do (println "else " structure) (kont structure))))) 

    (traverse-mobile-cps 
     [mobile kont] 
     (branch-weight-cps (left-branch mobile) 
         (fn [left-weight] 
          (branch-weight-cps (right-branch mobile) 
               (fn [right-weight] (kont (+ left-weight right-weight)))))))] 

    (traverse-mobile-cps mobile identity)))

在這一點上，我曾嘗試申請蹦牀，以維護我的籌碼。但有以下例外吹：

java.lang.ClassCastException: sicp_clojure.2_1_exercises_2_24_2_32$total_weight_STAR_$traverse_mobile_cps__6694$fn__6695$fn__6696$fn__6697 cannot be cast to java.lang.Number 
Numbers.java:126 clojure.lang.Numbers.add 
.../git/sicp-clojure/src/sicp_clojure/2_1_exercises_2_24_2_32.clj:185 sicp-clojure.2-1-exercises-2-24-2-32/total-weight*[fn] 
core.clj:5801 clojure.core/trampoline 
core.clj:5806 clojure.core/trampoline 
RestFn.java:439 clojure.lang.RestFn.invoke 
.../git/sicp-clojure/src/sicp_clojure/2_1_exercises_2_24_2_32.clj:186 sicp-clojure.2-1-exercises-2-24-2-32/total-weight*

使用蹦牀，以下的優秀link的代碼是：

(defn total-weight* [mobile] 
    (letfn 
    [(branch-weight-cps 
     [branch kont] 
     (let [structure (branch-structure branch)] 
     (if (mobile? (branch-structure branch)) 
      (do (println "then " structure) (kont (traverse-mobile-cps structure identity))) 
      (do (println "else " structure) (kont structure))))) 

    (traverse-mobile-cps 
     [mobile kont] 
     (branch-weight-cps (left-branch mobile) 
         (fn [left-weight] 
          (branch-weight-cps (right-branch mobile) 
               (fn [right-weight] #(kont (+ left-weight right-weight)))))))] 
    (trampoline traverse-mobile-cps mobile identity)))

最後一些樣本數據：

(def branch11 (make-branch 1 1)) 
(def branch22 (make-branch 2 2)) 
(def branch36 (make-branch 3 6)) 
(def branch43 (make-branch 4 3)) 

(def mobile11-43 (make-mobile branch11 branch43)) 
(def mobile36-22 (make-mobile branch36 branch22)) 

(def branch5m1143 (make-branch 5 mobile11-43)) 
(def branch7m3622 (make-branch 7 mobile36-22)) 
(def mobile5m1143-7m3622 (make-mobile branch5m1143 branch7m3622)) 

(total-weight* mobile5m1143-7m3622)

爲什麼它爆炸？

來源

2014-10-19 Andrea Richiardi

你問爲什麼它炸燬？你從來沒有真正保持你的問題。 – user100464 2014-10-19 18:55:14

對不起，是的，編輯。 – 2014-10-20 11:18:06

繼在我的崗位同樣的鏈接，我已經解決了把我的執行情況：

(defn total-weight* [mobile] 
    (letfn 
    [(branch-weight-cps 
     [branch kont] 
     (let [structure (branch-structure branch)] 
     (if (mobile? (branch-structure branch)) 
      (fn [] (traverse-mobile-cps structure kont)) 
      (fn [] (kont structure))))) 

    (traverse-mobile-cps 
     [mobile kont] 
     (branch-weight-cps (left-branch mobile) 
         (fn [left-weight] 
          (branch-weight-cps (right-branch mobile) 
               (fn [right-weight] #(kont (+ left-weight right-weight)))))))] 
    (trampoline traverse-mobile-cps mobile identity)))

來源

2014-10-22 10:01:19

SICP，延續傳球風格和Clojure的蹦牀

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