{"id":34014,"date":"2023-02-18T09:41:09","date_gmt":"2023-02-18T04:11:09","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-creating-a-method-in-common-lisp\/"},"modified":"2023-02-18T09:41:09","modified_gmt":"2023-02-18T04:11:09","slug":"solved-creating-a-method-in-common-lisp","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-creating-a-method-in-common-lisp\/","title":{"rendered":"[Solved] Creating a method in Common Lisp"},"content":{"rendered":"

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To create a function in common lisp you can use the defun<\/code> operator:<\/p>\n

(defun signal-error (msg)\n   (error msg))\n<\/code><\/pre>\n
Now you can call it like so:<\/p>\n
(signal-error \"This message will be signalled as the error message\")\n<\/code><\/pre>\n
Then you can insert it in your code like this:<\/p>\n
(print \"Enter number\") \n(setq number (read)) ;; <- note that you made a syntax error here.\n(cond ((< 1 number) (print \"Okay\"))\n      ((> 1 number) (signal-error \"Number is smaller than 1.\"))))\n<\/code><\/pre>\n
In your question you are asking about a method<\/code>. Methods operate on classes. For example imagine you have two classes human<\/code> and dog<\/code>:<\/p>\n
(defclass human () ())\n(defclass dog () ())\n<\/code><\/pre>\n
To create a method specific for each class you use defmethod<\/code>:<\/p>\n
(defmethod greet ((thing human))\n  (print \"Hi human!\"))\n\n(defmethod greet ((thing dog))\n  (print \"Wolf-wolf dog!\"))\n<\/code><\/pre>\n
Let’s create two instances for each class:<\/p>\n
(defparameter Anna (make-instance 'human))\n(defparameter Rex (make-instance 'dog))\n<\/code><\/pre>\n
Now we can greet each living being with the same method:<\/p>\n
(greet Anna) ;; => \"Hi human\"\n(greet Rex)  ;; => \"Wolf-wolf dog!\"\n<\/code><\/pre>\n
The process of common lisp knowing which method to execute is called “Dynamic dispatch”. Basically it matches the given argument’s classes to the defmethod<\/code> definitions.<\/p>\n
But I have no idea why you need methods in your code example.<\/p>\n
Here is how I would write the code if I was you:<\/p>\n
;; Let's wrap the code in a function so we can call it\n;; as much as we want\n(defun get-number-from-user ()\n  (print \"Enter number: \")\n  ;; wrapping the number in a lexical scope is a good\n  ;; programming style. The number variable is not\n  ;; needed outside the function.\n  (let ((number (read)))\n    ;; Here we check if the number satisfies our condition and\n    ;; call this function again if not.\n    (cond ((< number 1) (print \"Number is less than 1\")\n                        (get-number-from-user))\n          ((> number 1) (print \"Ok.\")))))\n<\/code><\/pre>\n
I would suggest you read “The Land of Lisp”. It is great book for beginners.<\/p>\n<\/p><\/div>\n
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            5<\/span> <\/p><\/div>\n<\/div>\n
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solved Creating a method in Common Lisp <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] To create a function in common lisp you can use the defun operator: (defun signal-error (msg) (error msg)) Now you can call it like so: (signal-error “This message will be signalled as the error message”) Then you can insert it in your code like this: (print “Enter number”) (setq number (read)) ;; <- note … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[1761,4531],"class_list":["post-34014","post","type-post","status-publish","format-standard","hentry","category-solved","tag-clisp","tag-common-lisp"],"yoast_head":"\n[Solved] Creating a method in Common Lisp - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-creating-a-method-in-common-lisp\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Creating a method in Common Lisp - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] To create a function in common lisp you can use the defun operator: (defun signal-error (msg) (error msg)) Now you can call it like so: (signal-error "This message will be signalled as the error message") Then you can insert it in your code like this: (print "Enter number") (setq number (read)) ;; <- note ... 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