Macro help

[Miki]

Greetings,

I need some help with the 1'st macro I'm writing.
I have many tests in the format

(deftest user-test
(let [session (test-session :authorization)]
(dispatcher "USER bugs" session)
(is (= (:user @session) "bugs"))
(is (= (get-one session) "+OK Hello bugs\n"))))

I've tried writing

(defmacro def-dispatcher-test [test-name state command & body]
`(deftest ~test-name
(let [session (test-session ~state)]
(dispatcher ~command session)
~@body)))

(def-dispatcher-test user-test :authorization "USER bugs"
(is (= (:user @session) "bugs"))
(is (= (get-one session) "+OK Hello bugs\n")))


But I get the following error;

Caused by: java.lang.Exception: Can't let qualified name: pop32imap-
test/session


I probably need to add some magic to the session expansion, but can't
figure out what.

Thanks,
--
Miki

[Sunil S Nandihalli]

use session# instead of session .. I think that should work.. try it..

--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clo...@googlegroups.com
Note that posts from new members are moderated - please be patient with your first post.
To unsubscribe from this group, send email to
clojure+u...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

[Sunil S Nandihalli]

Hi Miki,

 Just to elaborate on what I said before, session# creates a new symbol using gensym with a prefix session. It avoids accidental variable capture.

Sunil.

[Alan]

This. Macros, unless you do some gymnastics, always generate fully-
qualified names, which is a Good Thing. You can't bind qnames, in let
or function arguments or anywhere else. But clojure provides you with
a very useful var# syntax: this creates a new symbol which is
guaranteed to be unique, and lets you refer to it by that name
throughout the macro expansion. Here's a basic example:

(defmacro square [x]
`(let [val# ~x]
(* val# val#)))

(macroexpand '(square 3))

==> (let* [val__4209__auto__ 3]
(clojure.core/* val__4209__auto__ val__4209__auto__))


On Nov 8, 7:10 am, Sunil S Nandihalli <sunil.nandiha...@gmail.com>
wrote:

> use session# instead of session .. I think that should work.. try it..
>

> > clojure+u...@googlegroups.com<clojure%2Bunsu...@googlegroups.com>

[Leif Walsh]

Miki:

This is what Sunil is talking about:
http://en.wikipedia.org/wiki/Common_Lisp#Variable_capture_and_shadowing

The "symbol#" string is a part of how syntax-quote works. Read
http://clojure.org/reader#The Reader--Macro characters

On Mon, Nov 8, 2010 at 10:12 AM, Sunil S Nandihalli

--
Cheers,
Leif

[Miki]

Hello Sunil,

>  Just to elaborate on what I said before, session# creates a new symbol
> using gensym with a prefix session. It avoids accidental variable capture.

Thanks for the quick reply. However I *do* want the symbol name to be
"session" since the
code in "body" uses it.

All the best,
--
Miki

[Miki]

As in the below (which doesn't work).

(defmacro def-dispatcher-test [test-name state command & body]
`(deftest ~test-name
(let [session (test-session ~state)]
(dispatcher ~command session)
~@body)))

(def-dispatcher-test user-test :authorization "USER bugs"
(is (= (:user @session) "bugs"))
(is (= (get-one session) "+OK Hello bugs\n")))

[Laurent PETIT]

Hi,

session will be fully qualified. this is the default behavior.
If you really want it, then you can treat it as the result of the
unquoting of a value which resolves to a symbol.

So you'll use ~ to say you want the value of .... (quote session)
(quote session returns the symbol session when evaluated).

that is, use ~'session instead of just session.

HTH,

--
Laurent

2010/11/8 Miki <miki....@gmail.com>:

[Ken Wesson]

On Mon, Nov 8, 2010 at 2:01 PM, Laurent PETIT <lauren...@gmail.com> wrote:
> Hi,
>
> session will be fully qualified. this is the default behavior.
> If you really want it, then you can treat it as the result of the
> unquoting of a value which resolves to a symbol.
>
> So you'll use ~ to say you want the value of .... (quote session)
> (quote session returns the symbol session when evaluated).
>
> that is, use ~'session instead of just session.

Ugh.

What you really want in this case is a binding. Try this:

(defmacro def-dispatcher-test [test-name state command session-sym & body]
`(deftest ~test-name
(let [~session-sym (test-session ~state)]
(dispatcher ~command ~session-sym)
~@body)))

(def-dispatcher-test user-test :authorization "USER bugs" session

(is (= (:user @session) "bugs"))
(is (= (get-one session) "+OK Hello bugs\n")))

The added parameter just before the body specifies a name to bind the
session object to; this name can then be used in the body.

[Miki]

Great, that did it. Thanks.

On Nov 8, 11:01 am, Laurent PETIT <laurent.pe...@gmail.com> wrote:
> Hi,
>
> session will be fully qualified. this is the default behavior.
> If you really want it, then you can treat it as the result of the
> unquoting of a value which resolves to a symbol.
>
> So you'll use ~ to say you want the value of .... (quote session)
> (quote session returns the symbol session when evaluated).
>
> that is, use ~'session instead of just session.
>
> HTH,
>
> --
> Laurent
>

> 2010/11/8 Miki <miki.teb...@gmail.com>:

[Miki]

>> that is, use ~'session instead of just session.

> What you really want in this case is a binding. Try this:

> ...

> The added parameter just before the body specifies a name to bind the
> session object to; this name can then be used in the body.

This is good a well, but I prefer to dark magic suggested by Laurent :)

[Alan]

Yes, those are the two choices. Ken's suggestion is the cleanest, and
you definitely should do that in cases where it's not burdensome.
Here, where it's a macro for private testing, and you are certain not
to forget that it's magically binding session for you, then go ahead
and use Laurent's suggestion to create bindings.

[Laurent PETIT]

2010/11/8 Alan <al...@malloys.org>

Yes, those are the two choices. Ken's suggestion is the cleanest, and
you definitely should do that in cases where it's not burdensome.
Here, where it's a macro for private testing, and you are certain not
to forget that it's magically binding session for you, then go ahead
and use Laurent's suggestion to create bindings.

Ay, it was not a suggestion, just a specific answer to the specific question  :-)
 

On Nov 8, 11:38 am, Miki <miki.teb...@gmail.com> wrote:
> >> that is, use ~'session instead of just session.
> > What you really want in this case is a binding. Try this:
> > ...
> > The added parameter just before the body specifies a name to bind the
> > session object to; this name can then be used in the body.
>
> This is good a well, but I prefer to dark magic suggested by Laurent :)

[Alan]

Yeah, I know you wouldn't make such a dreadful recommendation without
prompting. I just want to make sure *he* knows that this is considered
a little smelly: Clojure gives you the power to do stuff like this,
and it's appropriate to use it sometimes, but you should be careful -
it's hard for a reason.

On Nov 8, 12:32 pm, Laurent PETIT <laurent.pe...@gmail.com> wrote:
> 2010/11/8 Alan <a...@malloys.org>

> > clojure+u...@googlegroups.com<clojure%2Bunsu...@googlegroups.com>

[Miki]

> I just want to make sure *he* knows that this is considered
> a little smelly: Clojure gives you the power to do stuff like this,
> and it's appropriate to use it sometimes, but you should be careful -
> it's hard for a reason.

I know it smells, and regularly I won't use such a thing (didn't like
these things when read about them in "On Lisp" as well).
However I think in the current situation it's the best solution.

Thanks again.