How to define a macro like defstruct?

Question

We define a structure like this way

(defstruct point
  x 
  y)

Then we get a function point-p

It seems easy to define a macro

(defmacro mac (fun-name)
  `(defun ,fun-name ()
     t))

But how can I add "-p" as a suffix on fun-name ? I think it may be something like

(defmacro mac (fun-name)
  `(defun ,(suffix ,fun-name) ()
     t))

suffix may be a function. So how in fact can I implement this ?

It's not exactly the same, but I think stackoverflow.com/q/24433035/1281433 may have an answer for you, or at least some helpful tips. — Joshua Taylor
– Joshua Taylor, Commented Mar 28, 2016 at 13:23

Sylwester · Accepted Answer · 2016-03-28 15:27:56Z

6

You simply use string to make a string out of your symbol. Do whatever you'd like with it and intern it to get an interned symbol you can use as identifier.

(defun suffix (symbol suffix)
  (intern (concatenate 'string (string symbol) (string suffix))))

(defmacro make-predicate (fun-name)
  `(defun ,(suffix fun-name '#:-p) ()
     t))
(make-predicate test)
(test-p) ; ==> t

NB: You have an error in your macro as you use the comma (unquote) inside an already unquoted expression.

edited Mar 28, 2016 at 15:27

answered Mar 27, 2016 at 3:39

Sylwester

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4 Comments

PuercoPop Over a year ago

Note that passing strings as suffix is going to have problems with readtable's whose case is modified

kennytilton Over a year ago

string-concat does not seem to be common-lisp. I use: (concatenate 'string ...etc)

Sylwester Over a year ago

@user115813 string-concat is imported into common-lisp-user in CLISP, but it's not a part of CL package. Changed to concatenate.

user6119377 Over a year ago

Thank you very much. I get it.

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