Clojure基于优先逻辑从地图中提取值

Question

我有一个函数想要根据优先顺序从地图中提取一个值.目前我正在将它作为一个嵌套的if结构,这是非常可怕的.我不得不相信有更好的方法.

虽然这项工作有更好的方法吗？

(defn filter-relatives [relatives]
    (if(contains? relatives :self)
         (relatives :self)
             (if(contains? relatives :north)
                 (relatives :north)
                     (if(contains? relatives :west)
                         (relatives :west)
                         (if(contains? relatives :east)
                             (relatives :east)
                             (relatives :south)
                         )
                     )
                 )
              )
          )
    )
)

Answer 1

(some relatives [:self :north :west :east :south])

Answer 2

关于什么:

(defn filter-relatives [relatives ordered-filters] 
    (first (filter identity (map relatives ordered-filters))))

样品运行:

user=> (filter-relatives {:a 1 :b 2 :c 3} [:z :b :a])                                                               
2

Answer 3

如果nil和false不是可能的值,其他答案都很好.如果是,你可以使用类似的东西

(if-let [e (some (partial find relatives)
                 [:self :north :west :east :south])]
  (val e)
  :no-key-found)

例如

(if-let [e (some (partial find relatives)
                 [:self :north :west :east :south])]
  (val e)
  :no-key-found)
; => false

(if-let [e (some (partial find {})
                 [:self :north :west :east :south])]
  (val e)
  :no-key-found)
; => :no-key-found