[racket] variables within macros

On 18/01/13 15:54, Matthias Felleisen wrote:
> Is there a single stumbling block or do you feel overwhelmed by
> the broad API to the syntax system? -- Matthias

It's a combination of the two...

My single stumbling block is "binding" identifiers -- I'm never sure if
I'm going to end up with an identifier referencing the same value/entity/
thing. This is because I'm not so used to passing the lexical context
around as the macro API (probably) demands.

So, in order to get my bindings right, I want to be sure I'm using
the right syntax-... calls. And this is where the breadth of the API
starts to overwhelm me.

There is also the fact that I'm "feeling around" the rest of the racket API
to understand the runtime-work that I want my macros to help me with.
Trouble is, the more I look into it "runtime" seems to be less like
"execute a function" and more like "run another macro"!



A concrete example is that I am trying to write a #lang language. Which, I
believe (from syntax_module-reader.html) requires me to:
(provide (except-out (all-from-out racket) #%module-begin)
          (rename-out [module-begin #%module-begin]))

I also want to (provide define/tested) which defines functions (with
racket's define), but also adds a unit test to the function... ala
(check-= (add2 2) 4 0 "something descriptive") Racket/raco provides the
facility to put that into a "test" module for unit testing.

But I find that because I'm tinkering with #%module-begin, simply adding
a (module+ test (check-= ...)) clause causes problems.

I *think* I'm doing something relatively simple; but there are enough
gotchas here to keep me going round in circles.

What I have just described is in:
   https://github.com/tim-brown/plt-games-racket-tested

the "minimal-..." code(*), when run leaves me with the error:
"check-=: unbound identifier in module in: check-="

To my mind there is nothing wrong! There is either something stupid that
I'm missing, or there is something that requires "knowledge of how all of
racket works together" (as described above).

This is a bit of a big bite to have taken out of the macro system, but I
have to start non-triviality somewhere. Equally, though extending the
language is something that Racket encourages; and as far as I can tell,
this is (or should be) a trivial extension.

Thank you for listening :-)

Tim

* the rest of the code shows evidence of me banging my head against various
   walls, may be instructive as to what extremes I have gone two, and may
   also provide amusement; but the minimal-... code is fundamentally where
   I'm coming stuck.



> On Jan 18, 2013, at 6:38 AM, Tim Brown wrote:
>
>> On 17/01/13 21:33, Greg Hendershott wrote:
>>>>> Greg Hendershott's pages may be of interest to you:
>>>>> http://www.greghendershott.com/fear-of-macros/
>>
>> Which is as close as I have come to "How to Design Macros" so far.
>>
>>>> I read that earlier, and it gave me the confidence to get stuck in...
>>>> maybe I read it again to give me the insight to know what I'm doing.
>>>
>>> Well it might help prepare you to understand something like Danny's
>>> solution. But unfortunately it doesn't specifically explain local
>>> expansion. That was only at the fuzzy edge of my own understanding.
>>> Still is: When I read something like Jens' code, my brain still hears
>>> "blah blah blah Ginger".
>>> <https://www.google.com/search?q=blah+blah+blah+ginger&tbm=isch>
>>
>> Do you _know_ how good it makes me feel that someone else "blah blah blah
>> Ginger"s with macros?
>>
>> Went through fear-of-macros AGAIN last night. I think I can cope with that!
>> It all sounds *so reasonable*... but everything anyone writes about macros
>> sounds *so reasonable*. Until I put the page down!
>>
>> I feel like one of those Zen disciples who just doesn't get it.
>> But quite often they do. After a while. So I'm keeping up hope.
>>
>> Tim
>>
>> --
>> Tim Brown <tim.brown at cityc.co.uk>  | City Computing Limited            |
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-- 
Tim Brown <tim.brown at cityc.co.uk>  | City Computing Limited            |
T: +44 20 8770 2110                | City House, Sutton Park Road      |
F: +44 20 8770 2130                | Sutton, Surrey, SM1 2AE, GB       |
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BEAUTY:  What's in your eye when you have a bee in your hand           |
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City Computing Limited registered in London No. 1767817.
Registered Office: City House, Sutton Park Road, Sutton, Surrey, SM1 2AE
VAT number 372 8290 34.