Clojure范围大小写宏

| 在R. Kent Dybvig的书“ The Scheme Programming Language，第4版”（第86页）中，作者为接受条件范围的
case
语句写了
define-syntax
（Scheme宏）。我以为我会在Clojure中尝试这个。 这是结果。 我该如何改善？对于范围运算符，我使用
:ii
，
:ie
，
:ei
和
:ee
，表示包含式，包含式，包含式，排除式， 和排他-排他。有更好的选择吗？ 我选择扩展为
cond
而不是离散的
if
语句，因为我觉得将来对
cond
宏的任何改进都会使我受益。 
(defmacro range-case [target & cases]
  \"Compare the target against a set of ranges or constant values and return
   the first one that matches. If none match, and there exists a case with the
   value :else, return that target. Each range consists of a vector containing
   3 terms: a lower bound, an operator, and an upper bound. The operator must
   be one of :ii, :ie, :ei, or :ee, which indicate that the range comparison
   should be inclusive-inclusive, inclusive-exclusive, exclusive-inclusive,
   or exclusive-exclusive, respectively.
   Example:
     (range-case target
                 [0.0 :ie 1.0] :greatly-disagree
                 [1.0 :ie 2.0] :disagree
                 [2.0 :ie 3.0] :neutral
                 [3.0 :ie 4.0] :agree
                 [4.0 :ii 5.0] :strongly-agree
                 42 :the-answer
                 :else :do-not-care)
   expands to
     (cond
       (and (<= 0.0 target) (< target 1.0)) :greatly-disagree
       (and (<= 1.0 target) (< target 2.0)) :disagree
       (and (<= 2.0 target) (< target 3.0)) :neutral
       (and (<= 3.0 target) (< target 4.0)) :agree
       (<= 4.0 target 5.0) :strongly-agree
       (= target 42) :the-answer
       :else :do-not-care)
    Test cases:
      (use \'[clojure.test :only (deftest is run-tests)])
      (deftest unit-tests
        (letfn [(test-range-case [target]
                                 (range-case target
                                             [0.0 :ie 1.0] :greatly-disagree
                                             [1.0 :ie 2.0] :disagree
                                             [2.0 :ie 3.0] :neutral
                                             [3.0 :ie 4.0] :agree
                                             [4.0 :ii 5.0] :strongly-agree
                                             42 :the-answer
                                             :else :do-not-care))]
      (is (= (test-range-case 0.0) :greatly-disagree))
      (is (test-range-case 0.5) :greatly-disagree)
      (is (test-range-case 1.0) :disagree)
      (is (test-range-case 1.5) :disagree)
      (is (test-range-case 2.0) :neutral)
      (is (test-range-case 2.5) :neutral)
      (is (test-range-case 3.0) :agree)
      (is (test-range-case 3.5) :agree)
      (is (test-range-case 4.0) :strongly-agree)
      (is (test-range-case 4.5) :strongly-agree)
      (is (test-range-case 5.0) :strongly-agree)
      (is (test-range-case 42) :the-answer)
      (is (test-range-case -1) :do-not-care)))
    (run-tests)\"
  `(cond
    ~@(loop [cases cases ret []]
        (cond
         (empty? cases)
         ret

         (odd? (count cases))
         (throw (IllegalArgumentException.
                 (str \"no matching clause: \" (first cases))))

         (= :else (first cases))
         (recur (drop 2 cases) (conj ret :else (second cases)))

         (vector? (first cases))
         (let [[lower-bound operator upper-bound] (first cases)
               clause (second cases)

               [condition clause]
               (case operator
                     :ii `((<= ~lower-bound ~target ~upper-bound) ~clause)
                     :ie `((and (<= ~lower-bound ~target)
                                (< ~target ~upper-bound)) ~clause)
                     :ei `((and (< ~lower-bound ~target)
                                (<= ~target ~upper-bound)) ~clause)
                     :ee `((< ~lower-bound ~target ~upper-bound) ~clause)
                     (throw (IllegalArgumentException.
                             (str \"unknown operator: \" operator))))]
           (recur (drop 2 cases) (conj ret condition clause)))

         :else
         (let [[condition clause]
               `[(= ~target ~(first cases)) ~(second cases)]]
           (recur (drop 2 cases) (conj ret condition clause)))))))
更新：这是修订版，其中包含了mikera和kotarak建议的更改： 
(defmacro range-case [target & cases]
  \"Compare the target against a set of ranges or constant values and return
   the first one that matches. If none match, and there exists a case with the
   value :else, return that target. Each range consists of a vector containing
   one of the following patterns:
     [upper-bound]                 if this is the first pattern, match any
                                   target <= upper-bound
                                   otherwise, match any target <= previous
                                   upper-bound and <= upper-bound
     [< upper-bound]               if this is the first pattern, match any
                                   target < upper-bound
                                   otherwise, match any target <= previous
                                   upper-bound and < upper-bound
     [lower-bound upper-bound]     match any target where lower-bound <= target
                                   and target <= upper-bound
     [< lower-bound upper-bound]   match any target where lower-bound < target
                                   and target <= upper-bound
     [lower-bound < upper-bound]   match any target where lower-bound <= target
                                   and target < upper-bound
     [< lower-bound < upper-bound] match any target where lower-bound < target
                                   and target < upper-bound
   Example:
     (range-case target
                 [0 < 1] :strongly-disagree
                 [< 2]     :disagree
                 [< 3]     :neutral
                 [< 4]     :agree
                 [5]       :strongly-agree
                 42          :the-answer
                 :else       :do-not-care)
   expands to
     (cond
       (and (<= 0 target) (< target 1)) :strongly-disagree
       (and (<= 1 target) (< target 2)) :disagree
       (and (<= 2 target) (< target 3)) :neutral
       (and (<= 3 target) (< target 4)) :agree
       (<= 4 target 5) :strongly-agree
       (= target 42) :the-answer
       :else :do-not-care)
    Test cases:
      (use \'[clojure.test :only (deftest is run-tests)])
      (deftest unit-tests
        (letfn [(test-range-case [target]
                                 (range-case target
                                             [0 < 1] :strongly-disagree
                                             [< 2]   :disagree
                                             [< 3]   :neutral
                                             [< 4]   :agree
                                             [5]     :strongly-agree
                                             42      :the-answer
                                             :else   :do-not-care))]
      (is (= (test-range-case 0) :strongly-disagree))
      (is (= (test-range-case 0.5) :strongly-disagree))
      (is (= (test-range-case 1) :disagree))
      (is (= (test-range-case 1.5) :disagree))
      (is (= (test-range-case 2) :neutral))
      (is (= (test-range-case 2.5) :neutral))
      (is (= (test-range-case 3) :agree))
      (is (= (test-range-case 3.5) :agree))
      (is (= (test-range-case 4) :strongly-agree))
      (is (= (test-range-case 4.5) :strongly-agree))
      (is (= (test-range-case 5) :strongly-agree))
      (is (= (test-range-case 42) :the-answer))
      (is (= (test-range-case -1) :do-not-care))))
    (run-tests)\"
  (if (odd? (count cases))
    (throw (IllegalArgumentException. (str \"no matching clause: \"
                                           (first cases))))
    `(cond
      ~@(loop [cases cases ret [] previous-upper-bound nil]
          (cond
           (empty? cases)
           ret

           (= :else (first cases))
           (recur (drop 2 cases) (conj ret :else (second cases)) nil)

           (vector? (first cases))
           (let [condition (first cases)
                 clause (second cases)

                 [case-expr prev-upper-bound]
                 (let [length (count condition)]
                   (cond
                    (= length 1)
                    (let [upper-bound (first condition)]
                      [(if previous-upper-bound
                         `(and (<= ~previous-upper-bound ~target)
                               (<= ~target ~upper-bound))
                         `(<= ~target ~upper-bound))
                       upper-bound])

                    (= length 2)
                    (if (= \'< (first condition))
                      (let [[_ upper-bound] condition]
                        [(if previous-upper-bound
                           `(and (<= ~previous-upper-bound ~target)
                                 (< ~target ~upper-bound))
                           `(< ~target ~upper-bound))
                         upper-bound])
                      (let [[lower-bound upper-bound] condition]
                        [`(and (<= ~lower-bound ~target)
                               (<= ~target ~upper-bound))
                         upper-bound]))

                    (= length 3)
                    (cond
                     (= \'< (first condition))
                     (let [[_ lower-bound upper-bound] condition]
                       [`(and (< ~lower-bound ~target)
                              (<= ~target ~upper-bound))
                        upper-bound])

                     (= \'< (second condition))
                     (let [[lower-bound _ upper-bound] condition]
                       [`(and (<= ~lower-bound ~target)
                              (< ~target ~upper-bound))
                        upper-bound])

                     :else
                     (throw (IllegalArgumentException. (str \"unknown pattern: \"
                                                            condition))))

                    (and (= length 4)
                         (= \'< (first condition))
                         (= \'< (nth condition 3)))
                    (let [[_ lower-bound _ upper-bound] condition]
                      [`(and (< ~lower-bound ~target) (< ~target ~upper-bound))
                       upper-bound])

                    :else
                    (throw (IllegalArgumentException. (str \"unknown pattern: \"
                                                           condition)))))]
             (recur (drop 2 cases)
                    (conj ret case-expr clause)
                    prev-upper-bound))

           :else
           (let [[condition clause]
                 `[(= ~target ~(first cases)) ~(second cases)]]
             (recur (drop 2 cases) (conj ret condition clause) nil)))))))
    
2020-02-05 4 条评论
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没有找到相关结果

    已邀请:

    傻寺俊擒

            我也会投票给我一些冗长但丑陋的东西。 
     (range-case target
   [(<= 0.0) (< 1.0)] :greatly-disagree
   [(<= 1.0) (< 2.0)] :disagree
   [(<= 2.0) (< 3.0)] :neutral
   [(<= 3.0) (< 4.0)] :agree
   (<= 4.0 5.0)       :strongly-agree
   42 :the-answer
   :else :do-not-care)
    这可能是一个可行的选择。     
    2020-02-05 0 0
    分享

    蓄荣糖些

            一些想法： 具有运算符的默认值（例如，“：ie \”在典型问题中可能是最自然的） 将一个边界默认设置为上一个或下一个上/下边界，这样您就无需重复相同的边界值。 考虑ifs而不是cond，以便您可以进行间隔二等分（如果您期望大量案例，那将是性能上的胜利） 一种替代方法是使宏在案例级别下工作，如下所示： 
    (cond
  (in-range target [0.0 1.0]) :greatly-disagree)
  (in-range target [1.0 2.0]) :disagree)
  ...)
    我个人喜欢这样，因为如果需要，您可以将范围测试与其他谓词混合。     
    2020-02-05 0 0
    分享

    磐剩

            我最初的看法： 
    (defn make-case [test val]
  (if (vector? test)
    `((and ~@(for [[lower comp upper] (partition 3 2 test)]
               (list comp lower upper)))
      ~val)

    (list :else val)))

(defmacro range-case [& cases]
  (let [cases (partition 2 cases)]
    `(cond ~@(mapcat (partial apply make-case) cases))))
    这需要对语法进行一些更改，如下所示： 
    (range-case 
 [0.0 <= x < 1.0] :greatly-disagree
 [1.0 <= x < 2.0] :disagree
 [2.0 <= x < 3.0] :neutral
 [3.0 <= x < 4.0] :agree
 [4.0 <= x <= 5.0] :strongly-agree
 [42 = x] :the-answer
 :else :do-not-care)
    我的版本可能违反了原始示例的精神，但是“优点”包括： 您不会硬编码为一个15英镑。您也不限于两个测试（较低的测试和较高的测试）。你可以做
    [0 < x <= y < 4 <= z]
    等。 语法更类似于数学比较符号。 Clojure的比较运算符可以自己作为参数传递。无需使用关键字并将其转换为比较运算符。这样，比较运算符就不会硬编码到函数中，而删除此间接层会使它的读取效果更好。 平等不再是特例。 劣势？ 
    x
    被重复了很多次。抓住ѭ17并将其放在顶部是否值得增加复杂性并降低灵活性？ 像您的原始示例一样，它使用中缀表示法。在前缀表示法的世界中，这可能会有些刺耳。 再说一遍，在这一点上，我们的宏所做的不只是将方括号更改为括号并“ 19”将一堆东西放在一起。所以我质疑您是否真的需要一个宏。 
    (defn ?? [& xs]
  (every? (fn [[lower comp upper]]
            (comp lower upper))
          (partition 3 2 xs)))

(cond
  (?? 0.0 <= x < 1.0) :greatly-disagree
  (?? 1.0 <= x < 2.0) :disagree
  (?? 2.0 <= x < 3.0) :neutral
  (?? 3.0 <= x < 4.0) :agree
  (?? 4.0 <= x <= 5.0) :strongly-agree
  (= 42 x) :the-answer
  :else :do-not-care)
        
    2020-02-05 0 0
    分享
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