defstruct

A more convenient form of define-record

Author

Dorai Sitaram, ported to CHICKEN by felix winkelmann, with improvements by Peter Bex

Repository

This egg is hosted on the CHICKEN Subversion repository:

https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/defstruct

If you want to check out the source code repository of this egg and you are not familiar with Subversion, see this page.

Defines a record type with the name NAME. SLOT may be a symbol or a list of the form (NAME INIT) where INIT is the default value of the slot (the INIT expression will only be evaluated when no value is given in the constructor procedure. It defaults to #f when none is provided).

The defstruct macro expands into predicate and accessor functions (just like the native define-record):

(import defstruct)

(defstruct point x y)

;; Creates code equivalent to the following:
(begin
  (define (point? x) ...)          ; is x a point?
  (define (point-x p) ...)         ; return x slot of point p
  (define (point-x-set! p n) ...)  ; change x slot of point p to n
  ...)

Additionally, a constructor procedure make-STRUCTNAME is defined, which accepts initialization values for all slots specified as keyword arguments:

(define p1 (make-point x: 99 y: 42))
 => ; a point with x = 99 and y = 42

If keywords for some slots are missing, their initialization values default to those supplied in the defstruct call, or else #f.

There are also two procedures update-STRUCTNAME and set-STRUCTNAME! defined for functionally and destructively updating selected values in an existing record:

(define p2 (update-point p1 x: 100))
p2
 => ; a point with x = 100 and y = 42

(= p1-x 99)
 => #t

(set-point! p1 x: 100)
(= p1-x 100)
 => #t

Finally, there are two conversion procedures for converting to and from alists, STRUCTNAME->alist and alist->STRUCTNAME:

(define p3 (alist->point '((x . 1) (y . 2))))
p3
 => ; a point with x = 1 and y = 2

(define p4 (make-point x: 123 y: 456))
(point->alist p4)
 => ((x . 123) (y . 456))

Bugs and limitations

This macro is unhygienic which, while resulting in concise syntax, has some drawbacks:

Just like with define-record you cannot use field names ending with -set! if you also have a similar field name not ending with -set!.
Just like with define-record you should avoid defining record types with a name that is a prefix of another record type's name in the same module, because that might cause naming clashes.
For the same reason, you should avoid defining record types named make or update.
You cannot use a field named >alist.

License

 Copyright (c) 2005, Dorai Sitaram
 Copyright (c) 2005, Felix Winkelmann (Chicken port)
 Copyright (c) 2008-2018, Peter Bex (Hygienic Chicken port + extensions)
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following
 conditions are met:
 
   Redistributions of source code must retain the above copyright notice, this list of conditions and the following
     disclaimer. 
   Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following
     disclaimer in the documentation and/or other materials provided with the distribution. 
   Neither the name of the author nor the names of its contributors may be used to endorse or promote
     products derived from this software without specific prior written permission. 
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS
 OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR
 CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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