clojure – 顺序中的可选元素

2023年9月6日 222次阅读

我正在尝试使用Prismatic / Schema匹配以下序列：

[{:n "some text"}] ; => valid

和

[{:k "some text"} {:n "some text"}] ; => valid

我尝试过的：

(s/def Elem3
  {:k s/Str})

(s/def Elem2
  {:n s/Str})

(s/def Elem
  [(s/optional Elem2 "elem2") Elem3])

(s/validate Elem [{:k "huji"}])
;; =>
;; Value does not match schema: [(named {:n missing-required-key, :k
;; disallowed-key} "elem2")]

(s/def Elem
  [(s/maybe Elem2) Elem3])

(s/validate Elem [{:k "huji"}])
;; =>
;; [(maybe {:n Str}) {:k java.lang.String}] is not a valid sequence
;; schema; a valid sequence schema consists of zero or more `one`
;; elements, followed by zero or more `optional` elements, followed by
;; an optional schema that will match the remaining elements.

(s/defrecord ElemOption1
  [elem3 :- Elem3])

(s/defrecord ElemOption2
    [elem2 :- Elem2
     elem3 :- Elem3])

(s/def Elem
  (s/conditional
   #(= 2 (count %)) ElemOption2
   :else ElemOption1))

(s/validate Elem [{:k "huji"}])
;; =>
;; Value does not match schema: (not (instance?
;;  peg_dsl.standard_app.ElemOption1 [{:k "huji"}]))

主要问题是我不明白写什么方式
允许省略指定向量的第一个元素的模式.
匹配上面两个向量的正确方法是什么？

最佳答案 你第一次尝试的问题是从一开始

可选意味着它期望{：k s / Str}或者没有任何东西,而且它正在看到

{：n s / Str},所以显然不对.

你的第二次尝试有两个问题.也许可以是价值
或者没有,但它需要存在.你也没有写过
序列模式正确.但是序列模式的问题
元素需要按顺序s / one * s / optional *和你
想要s /可选s / one.

你的第三次尝试更接近,使用条件,但你是
无法匹配,因为您没有验证的实例
记录,你正在验证地图.

解决方案如下所示：

(def ElemKNList [(s/one {:k s/Str} "k") (s/one {:n s/Str} "n")])
(def ElemNList [(s/one {:n s/Str} "n")])

(def Elem (s/conditional #(= 2 (count %)) ElemKNList 
                         :else ElemNList))

(s/validate Elem [{:k "huji"} {:n "huji"}])    
    => [{:k "huji"} {:n "huji"}]
(s/validate Elem [{:n "huji"}])
    => [{:n "huji"}]          
(s/validate Elem [{:k "huji"}])
    => ExceptionInfo Value does not match schema: [(named {:n missing-required-key, :k disallowed-key} "n")]  schema.core/validator/fn--18435 (core.clj:151)
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