[racket-dev] Identifier macros

Actually I would hope that section 1.2 (syntax model) in the reference would explain exactly how macros are invoked. Unless I'm missing something it never mentions exactly what syntax object is passed to the transformer function once a macro binding is observed.

It could either go in paragraph about transformer bindings in the 'expansion steps' section (1.2.3.2) or in the section specifically about transformer bindings (1.2.3.5). Something like

"If the binding appears at the head of a syntax object then the entire syntax object is passed as the argument to the transformer. In any other context only the syntax object for the binding itself is used as the argument."


On 12/05/2012 12:27 PM, Matthew Flatt wrote:
> At Wed, 5 Dec 2012 14:25:29 -0500, Carl Eastlund wrote:
>> 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. 
> Ah, that makes sense. Thanks!
>
>> 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?
>>>
>>>
>>>
> _________________________
>   Racket Developers list:
>   http://lists.racket-lang.org/dev