<html> <head> <style></style></head> <body class='hmmessage'><div dir='ltr'> Hello, is there a documented problem with (send e get-time-stamp) ? After upgrading from 5.1.2 to 5.2, suddenly all mouse events have a time-stamp of 0. Thanks Mathieu Paradis <div><div id="SkyDrivePlaceholder"></div>> Date: Wed, 1 Feb 2012 10:11:55 -0700 > From: ryan@cs.utah.edu > To: rac@ruediger-asche.de > CC: users@racket-lang.org > Subject: Re: [racket] macros in local namespaces?... > > On 02/01/2012 09:45 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! > > The easiest way is to use internal definitions instead: > > (let () > (define a 2) > (define b 3) > (define localc 4) > (define-syntax-rule (absfn varname) > (lambda (x) (+ (+ x localc) varname))) > (define afn (absfn a)) > (define bfn (absfn b)) > (afn (bfn 2))) > > Another way is to use letrec-syntaxes+values, as Matthias answered. > > Ryan > ____________________ > Racket Users list: > http://lists.racket-lang.org/users </div> </div></body> </html>