Something like this might be what you want:
(letrec-syntaxes+values ([(absfn)
(syntax-rules ()
[(_ varname) (lambda (x) (+ (+ x localc)
varname))])])
([(a) 2]
[(b) 3]
[(localc) 4]
[(afn) (absfn a)]
[(bfn) (absfn b)])
(afn (bfn 3)))
BUT, I strongly recommend abstraction the macro over both variables.
On Feb 1, 2012, at 11:45 AM, Rüdiger Asche wrote:
> Hi there,
>
> I'm trying to get a grip on macros. Here is a very simple Racket expression
> (1):
>
> (letrec [(a 2)
> (b 3)
> (afn (lambda (x) (+ x a)))
> (bfn (lambda (x) (+ x b)))]
> (afn (bfn 2)))
>
> Now I need a syntactic abstraction for afn and bfn. The following will do in
> first approximation (2):
>
> (define-syntax-rule (absfn varname) (lambda (x) (+ x varname)))
>
> (letrec [(a 2)
> (b 3)
> (afn (absfn a))
> (bfn (absfn b))]
> (afn (bfn 2)))
>
>
> However, it will fail due to scoping rules in the following example (3):
>
> (define-syntax-rule (absfn varname) (lambda (x) (+ (+ x localc) varname)))
>
> (letrec [(a 2)
> (b 3)
> (localc 4)
> (afn (absfn a))
> (bfn (absfn b))]
> (afn (bfn 2)))
>
> In other words, my syntactic extension absfn needs to be embedded in the
> namespace of the sorrounding expression (or as a "dumb" macro which simply
> does lexical replacement without considering scoping, but needless to say
> such a macro would be unhygienic).
> I suspect that letrec-syntax was meant for that purpose, but I can't figure
> out how the parameters to define-syntax-rule would translate to those of
> letrec-syntax.
>
> Does anyone have sample code for how to get (3) above to work?
>
> Thanks!
>
>
>
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