exception - 在 Clojure : "apply"t know how to create ISeq from: java. lang.Long 中使用 "Don' 函数时出错”

Question

在“Clojure in Action”(第 63 页)中处理以下示例:

(defn basic-item-total [price quantity] 
    (* price quantity))

(defn with-line-item-conditions [f price quantity] 
    {:pre [(> price 0) (> quantity 0)]
     :post [(> % 1)]} 
    (apply f price quantity))

评估 REPL:

(with-line-item-conditions basic-item-total 20 1)

导致抛出以下异常:

Don't know how to create ISeq from: java.lang.Long
  [Thrown class java.lang.IllegalArgumentException]

似乎在评估应用程序后抛出异常。

Answer 1

apply 的最后一个参数应该是 sequence of arguments .在您的情况下，用法可能看起来更像这样:

(defn with-line-item-conditions [f price quantity] 
    {:pre [(> price 0) (> quantity 0)]
     :post [(> % 1)]} 
    (apply f [price quantity]))

apply在处理参数列表时很有用。在您的情况下，您可以简单地调用该函数:

(defn with-line-item-conditions [f price quantity] 
    {:pre [(> price 0) (> quantity 0)]
     :post [(> % 1)]} 
    (f price quantity))