The macro stepper is your friend.
On Feb 2, 2012, at 2:50 AM, Rüdiger Asche wrote: > Thanks for the fast and on-the-spot response! > > Is there a way to run the preprocessor only so that I can see what code that > construction expands to before being passed to the read-eval loop? > > ----- Original Message ----- From: "Matthias Felleisen" <matth...@ccs.neu.edu> > To: "Rüdiger Asche" <r...@ruediger-asche.de> > Cc: <users@racket-lang.org> > Sent: Wednesday, February 01, 2012 6:03 PM > Subject: Re: [racket] macros in local namespaces?... > > > > 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! >> >> >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users > ____________________ Racket Users list: http://lists.racket-lang.org/users
