CODEWITHSUNDEEP
lispcommon-lisp
KoshVorlon
KoshVorlon

Reputation: 154

Looking to ignore certain characters if entered in a Common Lisp program

*Updated formatting of the code.

Good morning!

I'm teaching myself Common Lisp and I'm running into an issue where the program actually works, except if a certain character (",")is entered in as user input. The code (pretty short) is:

 (defun welcome ()
  (format t "Agent logged in. Status: Active, License to Kill: Active.~%~%"))


(defun getchoice3 ()
  (let ((choice  1))
  (format t  "~%Enter your password:  ")
   (let ((response (read)))
      (cond ((equal response '007)        
        (format t "~%~%Welcome James Bond, 007 ~%")(welcome))
        (t (format t "~%~%Incorrect Response!~%~%") (getchoice3))))))
           
(getchoice3)

If I update that code to try to catch the error, like:


(defun welcome ()
  (format t "Agent logged in. Status: Active, License to Kill: Active.~%~%"))


(defun getchoice3 ()
  (let ((choice  1))
  (format t  "~%Enter your password:  ")
   (let ((response (read)))
      (cond ((equal response '007)
          (if (#'symbolp (response))
          (getchoice3))
      (format t "~%~%Welcome James Bond, 007 ~%")(welcome))
      (t (format t "~%~%Incorrect Response!~%~%") (getchoice3))))))
           
(getchoice3)

It still works, and will go back to (getchoice3) on any symbol except ",". If I code it to look for the symbol explicitly:


(defun welcome ()
  (format t "Agent logged in. Status: Active, License to Kill: Active.~%~%"))


(defun getchoice3 ()
  (let ((choice  1))
    (format t  "~%Enter your password:  ")
    (let ((response (read)))
      (cond ((equal response '007)
         (if (/, (response))
         (getchoice3))
      (format t "~%~%Welcome James Bond, 007 ~%")(welcome))
      (t (format t "~%~%Incorrect Response!~%~%") (getchoice3))))))
           
(getchoice3)

It still fails on the "," symbol and tells me that symbol doesn't have a backquote.

Ultimately I want the program to accept any letter or number, but no symbols and if it's entered, just ignore it and ask for input.

Any thoughts? Thank you!

Upvotes: 0

Views: 221

Answers (3)

KoshVorlon
KoshVorlon

Reputation: 154

(This answer had a glaring error that was picked up by @ad absurdum - Thank you very much!)

(updated - rookie mistake has now been corrected - thank you again @ad-absurdum!)

I appreciate your assistance, especially @ad absurdum and @sds.

If anyone else needs to see the correct code, it's one change only, change (read) to (read-line), as they suggested:


(defun welcome ()
  (format t "~% Status: Logged In   Agent ID: 007   License to Kill:Active     Messages from M: 0~%~%"))


(defun getchoice3 ()
  (let ((choice 1))
    (format t  "~%Enter your password:  ")
    (let ((response (read-line)))
      (cond ((string-equal response "007")
         (format t "~%~%Welcome James Bond, 007 ~%")(welcome))
        (t (format t "~%Incorrect Reponse.~%") (getchoice3))))))

(getchoice3)

Thank you again for your assistance!

Upvotes: 0

Rainer Joswig
Rainer Joswig

Reputation: 139321

Your code to read user input:

(format ...)
...
(read)                ; input would be a Lisp data, using Lisp syntax

That should be something like this:

(format ...)
...
(finish-output ...)  ; make sure output happens before waiting for input
(read-line ...)      ; input would be text, returned as a string

Upvotes: 2

sds
sds

Reputation: 60054

You are reading text, not Lisp code/data, so you should be using read-line instead of read.

Upvotes: 4

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