關於Clojure函式引數用法，學習中一些總結，無廢話，直接看程式碼：

一、接受不定引數

;;接受不定引數
(defn f0[& pms]
    (println "params count=" (count pms) " type pms=" (type pms))
  (doseq [pm pms]
        (println pm)
    )
)

;;呼叫示例

;;呼叫示例
user=> (f0 "abc" 111 :err)
params count= 3  type pms= clojure.lang.ArraySeq
abc
111
:err
nil
user
 
=>

二、接受map引數，map可為空或缺失部分或全部關鍵字，解構出的引數值為nil

;;接受map引數，map可為空或缺失關鍵字，解構出的引數值為nil
(defn f1[pm  {:keys [key value]}]
 (println "pm->" pm)
 (println "key->" key)
 (println "value->" value) 
)

;;呼叫示例

user=> (f1 "abc" {:key "kk" :value 1})
pm-> abc
key-> kk
value-> 1
nil
user=> (f1 "abc" {:key "k2"})
pm
 
-> abc
key-> k2
value-> nil
nil
user=> (f1 "abc" {})
pm-> abc
key-> nil
value-> nil
nil
user=>

三、接受map引數,為解構引數設定預設值

;;接受map引數,為解構引數設定預設值
(defn f11[pm  {:keys [key value] :or {key "def-key" value "def-value"}}]
 (println "pm->" pm)
 (println "key->" key)
 (println "value->" value) 
)
 

;;呼叫示例

user=> (f11 "abc" {:key "kk" :value 1})
pm-> abc
key-> kk
value-> 1
nil
user=> (f11 "abc" {:key "k2"})
pm-> abc
key-> k2
value-> def-value
nil
user=> (f11 "abc" {})
pm-> abc
key-> def-key
value-> def-value
nil
user=>

四、可選命名引數

;;可選命名引數
(defn f2[pm & {:keys [key value]}]
 (println "pm->" pm)
 (println "key->" key)
 (println "value->" value) 
)

;;呼叫示例

user=> (f2 "abc" :key "kk" :value 1)
pm-> abc
key-> kk
value-> 1
nil
user=> (f2 "abc" :key "k2")
pm-> abc
key-> k2
value-> nil
nil
user=> (f2 "abc" )
pm-> abc
key-> nil
value-> nil
nil
user=>

五、有預設值的可選命名引數

;;有預設值的可選命名引數
(defn f22[pm & {:keys [key value] :or {key "def-key" value "def-value"}} ]
 (println "pm->" pm)
 (println "key->" key)
 (println "value->" value) 
)

;;呼叫示例

user=> (f22 "abc" :key "kk" :value 1)
pm-> abc
key-> kk
value-> 1
nil
user=> (f22 "abc" :key "k2")
pm-> abc
key-> k2
value-> def-value
nil
user=> (f22 "abc" )
pm-> abc
key-> def-key
value-> def-value
nil
user=>