[racket] Are there Racket structures similar to Common Lisp's?

From: Rouben Rostamian (rostamian at umbc.edu)
Date: Fri Aug 17 20:42:23 EDT 2012

Thank you all for the numerous comments and suggestions
regarding Lisp-style structures for Racket.  Following 
Danny Yoo's hint, I put together a perhaps kludgy
way of achieving the effect I was looking for.

Here it is:

;--- begin demo ----------------------------------------------------

; A /person/ is a structure (The '#:transparent' flag is optional):
(struct person (name age waist-size favorite-color) #:transparent)

; A /person/ constructor.  The argument /name/ is required; the
; other arguments are optional and are given default values of #f:
(define (make-person
          #:age [age #f]
          #:waist-size [waist-size #f]
          #:favorite-color [favorite-color #f])
  (person name age waist-size favorite-color))

; Let's make a person:
(make-person "John")
  => (person "John" #f #f #f)

; Another one:
(make-person #:age 35 #:waist-size 24 "Betty")
  => (person "Betty" 35 24 #f)

; Another one:
(define p (make-person #:age 35 "Alice" #:favorite-color "red"))

(person-name p)
  => "Alice"
(person-age p)
  => 35
(person-waist-size p)
  => #f

;--- end demo ----------------------------------------------------

Perhaps this can be jazzed up through the use of macros but
I haven't tried.


---- original message -------------------------------------------
From: Rouben Rostamian <rostamian at umbc.edu>
Date: Fri, 17 Aug 2012 00:09:34 -0400
To: users at racket-lang.org
Subject: [racket] Are there Racket structures similar to Common Lisp's?

Is there the equivalent of Common Lisp's /structure/ type in
Racket?  I looked through Racket's User Guide and Reference
manuals but did not see something similar, although it's
quite possible that I saw one but did not recognize it.

Specifically, here is what I want.  Consider the Common Lips
definition of a /person/ structure:

(defstruct person

Then create an instance:

(make-person :age 35
             :favorite-color "blue"
             :name "Bob")

The latter echos:


Let's note that the order of fields when invoking /make-person/
need not be the same as the order in which the /person/
structure is defined.

Furthermore, since /waist-size/ was not specified at invocation,
it was assigned NIL.

Rouben Rostamian

Posted on the users mailing list.