On 15.03.2006, at 09:08, Raphael Collet wrote:
Torsten Anders wrote:
Wouldn't it be worth discussing macros for Oz again?
It is not public, but at UCL we are thinking about it. But we are not
satisfied at all with what Denys proposed. We want to be able to
extend Oz with something that still looks like Oz. We want something
like
unless X<Y do {Show X} {Show Y} end
instead of
<<unless X<Y {Show X} {Show Y}>>
We have a student who is currently working at macros that allows to
define something like the first alternative. He even consider macros
with a recursive definition! This is extremely elegant for defining
loops. He defines a while loop more or less as
MACRO while Cond do Body end
if Cond then
Body while Cond do Body end
end
You don't need to know how to manipulate the syntax tree of your
program with such a definition. This part is done for you.
Nice! If writing macros becomes so easy, they may as become abused as
in Lisp ;-)
I believe there are two cases for which macros are often used:
* To write control structures which do not necessarily evaluate all
their arguments (like unless)
* To write special and convenient syntactic constructs which do not
have a function/procedure equivalent but could have one
In Oz, an example for the second case is the class <...> end
construct. The function Class.new supports only partly what the special
construct can do: You can not define methods with Class.new. Similar
restrictions can be found for similar constructors such as Functor.new
(no support for the keywords require and prepare).
Is there some fundamental reason, that creators like Class.new and
Functor.new only partly support what their special syntax counterpart
supports?
Having full creator procedures for every syntactic construct which can
be expressed by a procedure would reduce the need for macros.
Abstractions could be written as procedures instead (such as a function
creating a class).
Thank you very much!
Best,
Torsten
--
Torsten Anders
Sonic Arts Research Centre
Queen's University Belfast (UK)
www.torsten-anders.de
_________________________________________________________________________________
mozart-users mailing list
[email protected]
http://www.mozart-oz.org/mailman/listinfo/mozart-users
