clojure-spec：無法正確獲取函數的后置條件

Question

我正在嘗試在一個簡單的函數上計算Clojure規范 ，該函數可計算方矩陣中（行，列）位置的“鄰居”。 例如，對於下面給出的4x4矩陣，像元（1,1）的鄰居應為：（0,1），（1,0），（1,2），（2,1）。 甚至不在矩陣范圍內的像元（4,3）的鄰居應為（3,3）等。

函數的輸入是矩陣的大小和感興趣位置的（行，列）。 輸出是鄰居（行，列）的集合。 如果沒有鄰居，則此集合可以為空。

可以在“ Joy of Clojure，第二版，第94頁”中找到此問題；但是由於原始代碼對我來說太緊湊，因此對代碼進行了修改。然后，我嘗試對其進行說明，並檢查:pre和:post部分中的說明。

但是，我沒有使:post部分起作用。 運行測試用例時，我得到：

java.lang.ClassCastException: java.lang.Boolean cannot be cast
to clojure.lang.IFn

要改變什么？

(require '[clojure.spec.alpha :as s]
         '[clojure.test       :as t])

; ===
; Specs
; ===

(s/def ::be-row-col
       (s/coll-of integer? :count 2 :kind sequential?))
(s/def ::be-square-matrix-size
       (s/and integer? #(<= 0 %)))
(s/def ::be-row-col-vector
       (s/and (s/coll-of ::be-row-col) (s/int-in-range? 0 5 #(count %))))

; ===
; Function of interest
; ===

(defn neighbors [sqmsz rc]

     {:pre  [(s/valid? ::be-row-col rc)
             (s/valid? ::be-square-matrix-size sqmsz)] 
      :post [(s/valid? ::be-row-col-vector %)]
     }

     (let [ cross             [[-1 0] [1 0] [0 -1] [0 1]]
            in-sq-matrix?     (fn [x]
                                  (and (<= 0 x) (< x sqmsz)))
            in-sq-matrix-rc?  (fn [rc]
                                  (every? in-sq-matrix? rc))
            add-two-rc        (fn [rc1 rc2]
                                  (vec (map + rc1 rc2)))
            get-rc-neighbors  (fn [rc]
                                  (map (partial add-two-rc rc) cross)) ]
        (filter in-sq-matrix-rc? (get-rc-neighbors rc))))

; ===
; Put a collection of [row col] into an expected form
; ===
; this is used to run the test code

(defn formify [rc-coll]
   (let [ cmp (fn [rc1 rc2]
                  (let [ [r1 c1] rc1
                         [r2 c2] rc2 ]
                     (cond (< r1 r2) -1  ; sort by row
                           (> r1 r2) +1
                           (< c1 c2) -1  ; then by column
                           (> c1 c2) +1
                           true       0))) ]
      (vec (sort cmp rc-coll))))

; ===
; Testing
; ===

(defn test-nb [ sqmsz rc expected txt ]
   (do
      (t/is (= (formify (neighbors sqmsz rc)) expected) txt)
   ))

(test-nb  0  [0 0]  []  "Zero-size matrix, outside #1")    
(test-nb  0  [1 1]  []  "Zero-size matrix, outside #2")    
(test-nb  1  [0 0]  []  "One-size matrix, inside")    
(test-nb  1  [1 0]  [[0 0]]  "One-size matrix, outside")    
(test-nb  5  [0 0]  [[0 1] [1 0]]  "Testing top left")    
(test-nb  5  [1 0]  [[0 0] [1 1] [2 0]]  "Testing left edge")    
(test-nb  5  [1 1]  [[0 1] [1 0] [1 2] [2 1]]  "Testing middle #1")    
(test-nb  5  [2 2]  [[1 2] [2 1] [2 3] [3 2]]  "Testing middle #2")    
(test-nb  5  [3 3]  [[2 3] [3 2] [3 4] [4 3]]  "Testing middle #3")    
(test-nb  5  [4 4]  [[3 4] [4 3]]  "Testing btm right")    
(test-nb  5  [5 5]  []  "Testing outside #1")    
(test-nb  5  [5 4]  [[4 4]]  "Testing outside #2")    
(test-nb  5  [4 3]  [[3 3] [4 2] [4 4]]  "Testing btm edge")

Answer 1

您只是缺少#前綴以使您的匿名函數處於:post條件。 后置條件必須是可以獲取主題函數調用輸出的函數。

:post [#(s/valid? ::be-row-col-vector %)]

也可以改寫為：

:post [(fn [o] (s/valid? ::be-row-col-vector o))]

但是根據您的用例，您可能希望研究功能規格和instrument ，以代替:pre和:post條件。 我在這里寫了更多示例。