[racket] Newbie question: Teach Yourself Scheme in Fixnum Days - macros

From: Robby Findler (robby at eecs.northwestern.edu)
Date: Mon Apr 4 19:51:00 EDT 2011

On Mon, Apr 4, 2011 at 6:25 PM, Eli Barzilay <eli at barzilay.org> wrote:
> Four hours ago, Robby Findler wrote:
>> It looks like a great macro essay for a certain crowd (altho the
>> essay seems to insult that selfsame crowd; perhaps you are assuming
>> that that crowd is into S&M?).
> Where's the insult?  (I didn't mean any insult -- the only thing I can
> think of is the "nostalgia" reference, which is not an insult but the
> often expressed sentiment for "a simple system, like `defmacro'".)

Well, the scare quotes are a way to put down things, generally speaking.

>> Some comments:
>>  - I probably would have used #` in the second while macro. Yes, I
>> see you mention it later, but doing it at that point seems to fit
>> with what the reader's been given at that point
> Well, that's one point where the purpose of the document is different
> from a generic guide: my main goal was to write a quick intro to
> people who are familiar with `defmacro' -- so I wanted to make it very
> clear that it's the same kind of thing, only with wrapped sexprs
> instead of raw ones.  In this case, I think that the long route is
> better -- it shows that the extra tools (like #`) make things easier
> only after you're aware of what goes on (and the fact that there's no
> complicated magic involved, which is the frequent complain against
> `syntax-case').

Yes, and the second while macro is a fine place to say that, in my
opinion. Indeed, it seems like the most natural point to go to next
and then to continue later to say what is happening with the # on the
front. This is just how your text is already building (in a good way

>>  - it would be good if you did some kind of a computation at compile
>> time, preferably to demonstrate an interesting computation one
>> should want to do at compile time. Maybe a macro that embeds a
>> formatted source location into its output?
> Good idea, I'll add something.
>>  - cpp macros are, I believe, based on lexemes, not strings (so you
>> cannot have an unclosed string in a macro or something).
> Yeah, I couldn't find a way to phrase it better than stick a random
> "roughly" in.  Using "lexemes" is a good word to describe it, but it's
> a little too opaque -- any ideas for something more light?

"lexical tokens, like strings, parens, ..."?

>> At least nowadays they are.
> Yes -- I definitely have used `#define's with a double-quote opener.

I think you can still pass an arg to gcc to get the old behavior back.


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