Tim, I wholeheartedly agree. Scheme used to be plainly beautiful. Understand
lambda expressions, recursion and continuations, and everything else more or
less falls into place.
The Scheme part of Racket still is as cool, but the rest is a moloch. Just
syntactically understanding a Racket application requires deep digging into
the guts; when I first picked up Racket after a long absence of Scheme, I
just couldn't make heads or tails of all the #s, :s, ,s and and %s spread
all over the place (and I still need to look those up frequently when I
don't deal with something for a week or more). The macro system is even
worse for the reasons you describe. Nothing simple, beautiful or orthogonal
anymore. What a shame. Then take modules, phases and all the other bells and
whistles (some of which are actually useful, but most appear to be of
interest more to theoreticians than people involved in solving real
problems) and you end up with something that takes much more time to get the
tools to work right before you even get something relatively straightforward
accomplished with them.
It used to be the case that you could reduce a Scheme system to a very few
primitives and build the rest around it using syntactic extensions. That may
still be true in Racket, but dealing with the syntactic extensions
themselves requires learning a complete new and several times more complexe
language. Bummer. I just don't see how one would attract newcomers to Racket
when all the beauty is so obfuscated.
----- Original Message -----
From: "Tim Brown" <[email protected]>
To: "Matthias Felleisen" <[email protected]>
Cc: "Racket Users" <[email protected]>
Sent: Friday, January 18, 2013 6:36 PM
Subject: Re: [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 <[email protected]> | 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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Tim Brown <[email protected]> | 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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Registered Office: City House, Sutton Park Road, Sutton, Surrey, SM1 2AE
VAT number 372 8290 34.
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