2013/9/9 Dmitry Bogatov <kact...@gnu.org> > > Hello! > > Here is my implementation of for loop. I found lisp really extremely > flexible, but there is one problem --- more often then not I do not need > var part, so I do not care how it would be named --- all I care is that > it will not shadow any other bindings. > > I think I can do it(did not tryed it) with `define-macro` and uninterned > symbols, but it mean give up beauty of syntax-rules. > > Masters of syntax-rules and syntax-case, please give me peace of advice. > > (define-syntax for > (syntax-rules (in => as) > ([_ (pattern as var in list) exp ...] > [for-each (lambda (var) (match var (pattern exp ...))) list])))
Actually, the whole point of hygienic (syntax-rules) macros is that you don't need to worry about the names of variables. I often use a very similar python-like for loop macro in my projects: http://hg.gnu.org.ua/hgweb/slayer/file/554a63bd3c6c/guile-modules/extra/common.scm#l420 That code works just perfectly fine. IMO a bigger problem would be to break the referential transparency, so e.g. the definition like (define-syntax for (syntax-rules (in => break) ((_ pattern in list body ...) (call/cc (lambda(break) (for-each (match-lambda pattern body ...) list)))))) won't work as one might expect (i.e. you won't be able to write (break) inside a loop, because the "break" label gets renamed). The workaround is possible somehow, but I never had time to figure that out, so currently I just don't do breaks ;] Best regards, M.
