Common Lisp-如何汇总用户输入

Aaron 发表于 Dev

亚伦

我想采用一系列用户输入的整数，然后求和输入。例如，如果用户输入：

1 <return>
2 <return>
3 <return>
<return>

到目前为止，这是我的代码：

(defun stuff ()
  (format t "Enter a number: ")
  (let ((n (read)))
    (+ n)))

捣碎

实际上，此示例比应有的示例复杂得多，因为它需要进行多项操作（循环，读取输入和累加）。我将为您提供两种解决方案，一种是简便的方法，另一种是我个人的解决方案。首先简单的方法：

(defun stuff (&optional (acc 0)) ; An optional argument for keeping track of the sum.
  (if (y-or-n-p "Do you want to continue?") ; Ask if they want to continue
      (progn (format t "Enter a number: ")  ; If they say yes we need to ask them for the
             (stuff (+ acc (read))))        ; number, read it, add it to the sum, and
                                            ; continue. We need progn because we need to
                                            ; execute two pieces of code (format and stuff) in the if
      acc)) ; If they say no, then return the total sum

我将如何执行更高级的版本：

(defun stuff ()
  (loop while (y-or-n-p "Do you want to continue?") ; while they want to continue
        do  (format t "Enter a number: ")           ; print the prompt
        sum (parse-integer (read-line))))           ; read the line, parse the integer, and sum it

编辑：上一个版本的版本在新行上停止。

(defun stuff (&optional (acc 0))
  (let ((line (read-line)))
    (if (string= line "") ; If this line is the empty string
        acc               ; return the sum
        (stuff (+ acc (parse-integer line)))))) ; otherwise recur and sum the number on the line

(defun stuff ()
  (loop for line = (read-line)
        until (string= line "")
        sum (parse-integer line)))

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