輸出提示相互排列

Question

我在看書Practical Common Lisp。我輸入了第3章中顯示的簡單CD數據庫。請參見下文。當我運行(add-cds)程序的結果是包含在彼此頂部兩個提示提示（更確切地說，一個又一個提示，在同一行）：

(add-cds) 
=> Title: Artist: 

爲什麼這樣做呢？該程序應該給我Title:提示首先和Artist:提示只有在輸入Title:後跟換行符的值。我很確定我忠實地輸入了節目。我該如何解決？

(defvar *db* nil) 

(defun make-cd (title artist rating ripped) 
    (list :title title :artist artist :rating rating :ripped ripped)) 

(defun add-record (cd) (push cd *db*)) 

(defun prompt-read (prompt) 
    (format *query-io* "~a: " prompt) 
    (force-output *query-io*) 
    (read-line *query-io*)) 

(defun prompt-for-cd() 
    (make-cd 
    (prompt-read "Title") 
    (prompt-read "Artist") 
    (or (parse-integer (prompt-read "Rating") :junk-allowed t) 0) 
    (y-or-n-p "Ripped [y/n]"))) 

(defun add-cds() 
    (loop (add-record (prompt-for-cd)) 
     (if (not (y-or-n-p "Another? [y/n]: ")) (return)))) 

Answer 1

發生的事情是，(add-cds)之後的換行符被留在輸入流中（因爲REPL停止只要它看到匹配的右括號閱讀），所以第一個read-line被讀取爲空白行並立即返回。致電clear-input，然後致電read-line忽略此操作並等待新輸入。

(defun prompt-read (prompt) 
    (format *query-io* "~a: " prompt) 
    (force-output *query-io*) 
    (clear-input *query-io*) 
    (read-line *query-io*))