[racket] Macro defining functions question

On May 15, 2014, at 12:30 PM, Asumu Takikawa <asumu at ccs.neu.edu> wrote:

> On 2014-05-15 15:24:01 -0400, Matthias Felleisen wrote:
>>> Incidentally the macro stepper shows bar in the define differently
>>> colored from the rest of the definition, while it shows y in the baz
>>> definition as being differently colored. I’m not sure what the color
>>> key is though!
>> 
>> Click on the identifiers to inspect their properties.
> 
> BTW, you may need to adjust your macro stepper settings to see this.
> 
> Stepper->View syntax properties.
> 
> Cheers,
> Asumu

Thanks guys! That gets me a bit closer to wrapping up the diversion I undertook playing around with generics. There might be a better way to do this, but what I was interested in was a way of providing the generic binding for helper functions. So far I came up with this (although wouldn’t it be nice if there was just an “anaphoric-style it” we could make use of built into the dispatch?)

#lang racket

(require (for-syntax racket/syntax)
         racket/generic)

(define-syntax (helper-bind-gen stx)
  (syntax-case stx ()
    [(_ g)
     (with-syntax ([gen:name (format-id stx "~a" #'g)]
                   [parm:name (format-id stx "parm:~a" #'g)]
                   [bind:name (format-id stx "bind:~a" #'g)]
                   [with:name (format-id stx "~a" 'with-bind)])
       #'(begin
           (define parm:name (make-parameter #f))
           (define-syntax bind:name
             (syntax-id-rules ()
               [(set! _ e) (set! parm:name (make-parameter e))]
               [(_ args (... ...)) ((parm:name) args (... ...))]
               [_ (parm:name)]))
           (define-syntax (with:name stx)
             (syntax-case stx ()
               [(_ g (f args (... ...)))
                (with-syntax ([parm:name (format-id stx "parm:~a" #'g)])
                  #'(parameterize ([parm:name g]) (f args (... ...))))]))))]))

(define-generics w
  [set-x! w v])

(struct foo (x)
  #:mutable
  #:methods gen:w
  [(helper-bind-gen w)
   (define (helper v) (set-foo-x! bind:w v))
   (define (set-x! w v) (with-bind w (helper v)))])

(define f1 (foo 3))
(set-x! f1 10)
(foo-x f1)

-Kevin