[Python-Dev] A Hygienic Macro System in Python?

[Neil Schemenauer]

Jeremy Hylton wrote:
> There has not been much interest in macros of any sort,
> although there have been a few threads on comp.lang.python
> recently.  It may be that a few motivating examples would
> make clear why we should be interested :-).  

I'm interested.  It's hard though in a language with a lot of syntax,
maybe no even worth doing.  Dylan macros are a lot less powerful than
Common Lisp macros.

Two applications immediately come to mind.  First, Quixote's unit test
module (now known Sancho).  Right now you have to write:

    self.test_val("foo.dosomething()", 2)

It would be nice if you could instead write:

    test_val(foo.dosomething(), 2)

Secondly, Quixote's PTL compiler.  If Python had macros I wouldn't have
written it.  Take a look at the HTML Generation facility that comes with
Allegroserve¹.  

I think I understand why macros work so well with Common Lisp.  In
Common Lisp, the AST is really a list.  The AST is easy to read and
write and it's easy to make macros transform it.  That gives Common Lisp
programmer's an amazing amount of power.  Maybe Guido thinks it gives
them too much.  Myself, I don't know.  Most of the time you don't need
macros but when you do you really do.

  Neil


¹http://allegroserve.sourceforge.net/htmlgen.html