Also, there are some more modern alternatives to `with-steps`. I particularly like the `staged` and `slide/staged` macros, which you can read about here: http://docs.racket-lang.org/unstable-gui/Slideshow_Presentations.html#%28part._.Staged_.Slides%29
Sam On Wed Jan 21 2015 at 9:47:28 AM Matthew Flatt <mfl...@cs.utah.edu> wrote: > At Wed, 21 Jan 2015 13:04:11 +0000, Reuben Thomas wrote: > > Since I have a lot of slides like this, I want to write a macro. I tried: > > > > #lang slideshow > > > > (require slideshow/step) > > > > (define-syntax-rule (correct from to) > > (lt-superimpose > > ((vonly before) (t from)) > > ((vonly after) (t to)))) > > > > (void > > (with-steps > > (before after) > > (slide > > (correct "With" "By")))) > > > > but I get the error: > > > > vonly: unbound identifier in module in: vonly > > > > I've experimented with various types of quoting and unquoting, and tried > > define-simple-macro instead of define-syntax-rule, but I'm forced to > admit > > I don't know what I'm doing! > > > > I know that vonly is special and is bound non-hygienically inside the > scope > > of the with-steps; how do I reference it correctly in a macro? > > You're right that the essential problem is that `with-steps` introduces > binding no-hygienically. Non-hygienic macros don't compose nicely. > > If `with-steps` were written in modern Racket, then it would be > hygienic, where `vonly`, etc., are bindings that take their meaning > as syntax parameters from an enclosing `with-steps`. Fortunately, it's > possible to implement a more modern `with-steps` using the existing one. > > Use the enclosed "new-step.rkt" in place of `slideshow/step`, and then > your `correct` macro will work. > ____________________ > Racket Users list: > http://lists.racket-lang.org/users >
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