Abdulaziz Ghuloum wrote:
On May 23, 2009, at 3:37 PM, Eduardo Cavazos wrote:
So I can do:
(define rgba-red-change!
(field-changer (record-type-descriptor rgba) 'red))
I think that's more or less the way to go about this. But if anyone
has any suggestions, they're welcome.
You can write
(define-record-type+changers rgba
(fields (mutable red)
(mutable green)
(mutable blue)
(mutable alpha)))
which translates to a define-record-type followed by your set of
additional definitions.
In addition to per field changers, I'm also interested in a record
cloner and record assigner. This takes care of the cloner and assigner:
(define-syntax define-record-type++
(syntax-rules (fields mutable)
( (define-record-type++ (name constructor predicate cloner assigner)
(fields (mutable field accessor mutator)
...))
(begin
(define-record-type (name constructor predicate)
(fields (mutable field accessor mutator)
...))
(define (cloner record)
(constructor (accessor record)
...))
(define (assigner a b)
(mutator a (accessor b))
...)) )))
And using it to make the rgba record type:
(define-record-type++ (rgba make-rgba rgba? rgba-clone rgba-assign!)
(fields (mutable red rgba-red rgba-red-set!)
(mutable green rgba-green rgba-green-set!)
(mutable blue rgba-blue rgba-blue-set!)
(mutable alpha rgba-alpha rgba-alpha-set!)))
Another variant with support for cloner, assigner, and changers:
(define-syntax define-record-type++
(syntax-rules (fields mutable)
( (define-record-type++ (name constructor predicate cloner assigner)
(fields (mutable field accessor mutator changer)
...))
(begin
(define-record-type (name constructor predicate)
(fields (mutable field accessor mutator)
...))
(define (cloner record)
(constructor (accessor record)
...))
(define (assigner a b)
(mutator a (accessor b))
...)
(define (changer record procedure)
(mutator record (procedure (accessor record))))
...
) )))
And the example:
(define-record-type++ (rgba make-rgba rgba? rgba-clone rgba-assign!)
(fields (mutable red rgba-red rgba-red-set! rgba-red-change!)
(mutable green rgba-green rgba-green-set! rgba-green-change!)
(mutable blue rgba-blue rgba-blue-set! rgba-blue-change!)
(mutable alpha rgba-alpha rgba-alpha-set! rgba-alpha-change!)))
At about that point syntax-case start to look attractive. :-) Or some
editor macros.
Some people, when confronted with a problem, think "I know, I'll use
syntax-case." Now they have two problems.
;-)
Really though, all the code for handling the define-record-type syntax
is in 'psyntax.expander.ss'. It's a shame that this isn't available for
reuse in cases like this where there's a need to extend a macro. Or make
a new macro with similarish syntax. Well, yeah, I can cut and paste...
Ed
