<div class="gmail_extra">#|An update: here is what the macro looks like now.|# (define-syntax (define-property stx) (define make-id (lambda (template . ids) (define str (apply format template (map syntax->datum ids))) (datum->syntax stx (string->symbol str)))) (syntax-parse stx [((~literal define-property) name:id init-value) (with-syntax ([getter-name (make-id "get-~a" #'name)] [setter-name (make-id "set-~a" #'name)]) #'(begin (define name init-value) (define/public (setter-name value) (set! name value)) (define/public (getter-name) name)))] [((~literal define-property) name:id init-value ((~literal get:expr) get-body)) (with-syntax ([getter-name (make-id "get-~a" #'name)]) #'(begin (define name init-value) (define/public (getter-name) get-body)))] [((~literal define-property) name:id init-value ((~literal set) (setter-vars:id ...) set-body:expr)) (with-syntax ([setter-name (make-id "set-~a" #'name)]) #'(begin (define name init-value) (define/public (setter-name setter-vars ...) set-body)))] [((~literal define-property) name:id init-value ((~literal get) get-body) ((~literal set) (setter-bindings:id ...) set-body:expr)) (with-syntax ([getter-name (make-id "get-~a" #'name)] [setter-name (make-id "set-~a" #'name)]) #'(begin (define name init-value) (define/public (setter-name setter-bindings ...) set-body) (define/public (getter-name) get-body)))])) Somewhat like <a href="http://msdn.microsoft.com/en-US/library/w86s7x04%28v=vs.80%29.aspx">http://msdn.microsoft.com/en-US/library/w86s7x04%28v=vs.80%29.aspx</a>, but with mandatory initialization expressions for each property. -Patrick <div class="gmail_quote">On 25 April 2012 10:10, Asumu Takikawa <<a href="mailto:asumu@ccs.neu.edu" target="_blank">asumu@ccs.neu.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> <div>On 2012-04-25 03:19:46 -0400, Patrick Mahoney wrote: > I'm looking to define a macro that extends the forms within a racket/class > class%. In particular, I would like a form to define a C# like class > language form property, that implements the getters and setters for an > initialized field automatically. </div>FYI, `get-field` and `set!-field` already allow you to get and set any public fields on an object. <div> > (define-syntax (define-property syntax) > (syntax-parse syntax > [((~literal define-property) name:id init-value) > > #'(define name init-value) > (define/public (set-name! init-value) > (set! name init-value)) > (define/public (get-name) > name)])) </div>So this macro won't quite work as written. Here's an alternative that will at least run (but still won't work as you expect): (define-syntax (define-property stx) (syntax-parse stx [(_ name:id init-value) #'(begin (define name init-value) (define/public (set-name! new-val) (set! name new-val)) (define/public (get-name) name))])) One issue was that you were using `syntax` as the argument to this transformer, which won't work because you end up shadowing `syntax`, which is needed to write the template. I changed it to `stx`. Secondly, you need to use `begin` to splice all of the definitions together. Note that this still doesn't work though. The `set-name!` and `get-name` will be introduced as is (or hygienically renamed) and won't use the name of the field as you might want. To do that, you might want to write `define-property` so that it takes get/set method names as arguments.[1] [1]: otherwise you need to unhygienically introduce a binding, which is best to avoid unless you know what you are doing. <div> > define/public: use of a class keyword is not in a class top-level in: > (define/public (set-name! init-value) (set! name init-value)) </div>You probably got this error by trying out the macro outside of a class or because you weren't splicing the definition quite right. Cheers, Asumu </blockquote></div> </div>