[racket-dev] Identifier macros

On looking back, my confusion was not entirely due to the documentation,
but partly from my own expectations coming in to it.  If I just look up
"identifier macro", trying to figure out how to write one, I get a link to
section 16.1.5.  This does not directly state the context involving
syntax-rules; it instead describes an identifier macro simply as "...works
in any expression".  The documentation then goes on to present
syntax-id-rules as a mechanism for identifier macros, presenting set!
transformation as well.  So while it doesn't explicitly state that set!
transformers and identifier macros are the same thing, it does appear to
imply it and doesn't clarify the matter.  If we're going to use "identifier
macro" as an indexed technical term, we should probably have a more precise
discussion of it in the reference manual as well that spells out how these
things work.  I know I wasn't the only one surprised to find out that
ordinary define-syntax & syntax-case / syntax-parse macros can expand (what
most people would call) identifier macros.  The only way I can figure this
out in the documentation is from a very close reading of the low-level
expansion model, which is not written terribly plainly to begin with.

--Carl

Carl Eastlund

On Wed, Dec 5, 2012 at 2:12 PM, Matthew Flatt <mflatt at cs.utah.edu> wrote:

> At Wed, 5 Dec 2012 09:41:37 -0500, Matthias Felleisen wrote:
> >
> > I think two additions/refinements would be good here:
> >
> > 1. The section on identifier macros in the Guide (16.1.5) should mention
> that
> > define-syntax introduces short-hands for identifiers, period.
>
> I think "a `define-syntax' that binds to a procedure of one argument"
> is what you mean --- but section 16.1 is about `syntax-rules' and
> `syntax-id-rules', not procedures as transformers.
>
> Improving the start of 16.2 along these lines makes sense, along with a
> better connection to 16.1. Or maybe you're suggesting a different
> organization than the current 16.1--16.2 split?
>
> I'm still unclear on the specific text that confused Carl, though. Was
> it 16.1?
>
>
>
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