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Editorial Team
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Asked: 2026-06-14T00:30:57+00:00

I am trying to get started with Lisp and I have some (messy) code

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I am trying to get started with Lisp and I have some (messy) code that i want to be able to ask the user for a title and url.

Save them in a variable, and then print them out when called. I am running into troubles though. First of all i don’t know how to compile my program to run it. Also, the one time when i did run it i got an error about the variable title being uncalled. Can anyone help me with either of these things? Sorry i can’t give you more information about the error.

;;Define a function called make-cd that takes four parameters
(defun make-url( title url ))
    (list :title title :url url)

;;In the make-url function create a plist that takes the passed values


;; Define global variable db and set its value to nil
(defvar *db* nil)

;; Define a function that takes one paramter and pushes it to the make-url func.
;;(defun add-url (url) (push url *db*))

;; Define a function that takes the *db* variable and makes the output pretty
(defun dump-db ()
   (dolist (url *db*)
       (format t "~{~a:~10t~a~%~}~%" url)))

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

  1. Editorial Team

    The code you have provided contains errors and will not compile. The error is in your definition of make-url. The proper definition should be:

    (defun make-url( title url )
      (list :title title :url url))

    Notice the difference in parenthesis placements.

    In your code you had an additional parenthesis following the parameter list. This closed the defun, causing make-url to be evaluated as a function with no body. The next line was then evaluated as a call to the built-in function list. The arguments were evaluated, and an error was encountered when it attempted to find a value for title. There is no binding in the global environment, a binding for title only exists within the body of make-url.

    Also, your definition of add-url is commented out. A semi-colon begins a comment in Lisp.

    How to compile and run your program depends on what compiler you are using. If you are using SBCL the function is sb-ext:save-lisp-and-die. A simple program like this would usually be run in a Read-Eval-Print-Loop(REPL), and most compilers will enter one when started. If you have SBCL installed you can start a repl by entering the command ‘SBCL’ to the command prompt. If your code is in an external file you can then load that using Load.

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