Short list with things to finish for D2

[Bill Baxter]

On Mon, Nov 23, 2009 at 5:32 AM, Steven Schveighoffer
<schveiguy at yahoo.com> wrote:
> On Mon, 23 Nov 2009 07:38:32 -0500, Bill Baxter <wbaxter at gmail.com> wrote:
>
>> On Mon, Nov 23, 2009 at 3:12 AM, Don <nospam at nospam.com> wrote:
>>
>>>> This sounds like a job for better mixin syntax.
>>>> .
>>>> So let "template#(args)" be equivalent to "mixin(template!(args))".
>>>>
>>>> Then you can do
>>>>
>>>> auto statement = db.execute#(`select $visitcars.name from table where
>>>> $visitcars.id > 100 && $visitcars.surname Like "A*"`);
>>>
>>> Yeah, something like that. Or it could mixin automatically. eg if
>>> macro foo(args...)
>>> foo(args) meant  mixin(foo(args)).
>>
>> This is what I've been thinking too.
>> But we might want there to be more to a macro than that.  For instance
>> most macro parameters are strings and the '(string this, string that,
>> string theOther)', list of parameters doesn't look so great.  And
>> requiring the strings to be quoted on the calling side, also makes the
>> call side rather ugly.  It may be better to have arguments
>> automatically convert to some sort of AST type which supports some
>> introspection, and can be converted back to a string of code easily.
>>
>> So I think jumping on just making macro mean "mixin automatically"
>> right now may limit our future choices too much.
>
> What about this:
>
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.learn&article_id=17853


Quoting from there:
"""
macro doit(x, y, z) mixin("x" ~ "y" ~ "z"); // allow easy syntax for
quoting parameters, since mixins are all about stringification.

doit(a, b, c) => mixin("abc");
"""

What happens if you want to have the string "x", just a plain x, in the mixin?

Other than that, I think I don't know enough about the lessons to be
learned from Lisp, Scheme, and Nemerle.  I'd like to study more how
macros work in those systems before I'd feel comfortable committing to
any particular design.  For instance what's the best way to handle
hygene issues mentioned here:
http://en.wikipedia.org/wiki/Hygienic_macro .

There are probably some hygene issues there that should be considered
for template mixins too.  For instance it's a long-standing issue that
if you use a mixin from a library, you must import all the modules
that mixin depends on, which breaks a kind of encapsulation of the
mixin.  Mixins are probably also subject to the kind of environmental
hygene problem described on that page, where a common function
redefined in the current scope alters the intended behavior of the
mixin.

I think Walter had intended template mixins to take the place of
macros.  They offer some features of macros but not all.  So once real
macros exist, I wonder if there will be any real reason for them to
continue existing.

--bb