Thanks Matthias, thats a lot cleaner than my version. On 2011-07-28, at 1:19 PM, Matthias Felleisen wrote:
> > You could fake it: > > (require (for-syntax syntax/parse)) > > ;; Syntax SyntaxList SyntaxList -> [Listof (list String Syntax Syntax)] > ;; create association list mapping field names to getters and setters > [option] > (define-for-syntax (field-association-list sn getters setters) > (define sn-str (+ (string-length (symbol->string (syntax->datum sn))) 1)) > (define getters-lst (syntax->list getters)) > (define setters-lst (syntax->list setters)) > (for/list ((x getters-lst) (y setters-lst)) > `(,(substring (symbol->string (syntax->datum x)) sn-str) ,x ,y))) > > (define-syntax (increment! stx) > (syntax-parse stx > [(_ s sn:id fn:id i) > (with-syntax ([(_ _ _ getters setters _) (extract-struct-info > (syntax-local-value #'sn))]) > (define gets-sets (field-association-list #'sn #'getters #'setters)) > (define get-set-f (assoc (symbol->string (syntax-e #'fn)) gets-sets)) > (cond > [(boolean? get-set-f) (raise-syntax-error #f "unknown field-name: > ~a" stx)] > [else > (define-values (_ getter setter) (apply values get-set-f)) > (if (boolean? setter) > (raise-syntax-error #f (format "~s not mutable" (syntax-e > #'fn)) stx) > #`(#,setter s (+ (#,getter s) i)))]))] > [(increment! s sn fn) #'(increment! s sn fn 1)])) > > > > > > On Jul 28, 2011, at 3:08 PM, Tom McNulty wrote: > >> >> On 2011-07-28, at 12:43 PM, Eli Barzilay wrote: >> >>> 7 minutes ago, Matthias Felleisen wrote: >>>> >>>> On Jul 28, 2011, at 2:10 PM, Tom McNulty wrote: >>>> >>>>> I was hoping that I could locate the getter (and setter) with just >>>>> the field and structure type but that information doesn't seem to >>>>> be possible. >>> >>> Ah, you're right. >>> >>> >>>> I don't understand your request but if you are giving me the >>>> structure name and the structure field, you can write a >>>> context-sensitive macro: >> >> Matthias: Sorry I worded that poorly. I was looking to retrieve the >> accessors and mutators from the structure and field names in the macro, but >> that information is not retained. >> >>> >>> That's how Tom started, and I didn't follow the intention of using the >>> field name and suggested using the struct info. >>> >>> But the real thing that you (Tom) are fighting with is trying to use >>> field names, where the struct info is disregarding that and keeps >>> around just the getter and setter names. >> >> Other than possibly better error messages, I'm not sure then that the >> struct-info approach provides much (any?) benefit; for it still relies on >> knowing the accessor name. It also seems that accessors/mutators that do >> not follow the usual [set-]struct-field naming seem to be a rarity >> (certainly in my code). >> >>> Looks to me like a better >>> approach would be to use the getter names instead -- possibly with a >>> macro that makes more convenient getters? >> >> I thought about this approaching, using something similar to the key-word >> structures here, >> http://lists.racket-lang.org/users/archive/2010-December/043340.html >> but decided it'd be better to make something that works with vanilla >> structs. >> >> >> Thanks, >> >> - Tom. >> >>> >>> -- >>> ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay: >>> http://barzilay.org/ Maze is Life! >> > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
