On 2007-06-21, Douglas Alan <[EMAIL PROTECTED]> wrote:
> Steven D'Aprano <[EMAIL PROTECTED]> writes:
>> On Wed, 20 Jun 2007 17:23:42 -0400, Douglas Alan wrote:
>>> Macros are a way to abstract syntax the way that objects are
>>> used to abstract data types and that iterators and generators
>>> abstract control, etc.
>
>> But why is the ability to abstract syntax good?
>
> It allows the community to develop language features in a
> modular way without having to sully the code base for the
> language itself.
That's not an advantage exclusive to macros, though.
Some time last week I found myself writing the following thing in
Python:
def do_until(body, test):
body()
while not test():
body()
I don't remember why I thought I needed it; it had to do with
getting really annoyed with the code repetition needed for
certain kinds of while loops in Python.
I deleted it right after I tried to use it the first time. Using
it is more cumbersome than simply repeating myself, due to syntax
limitations of Python.
Until iterators came along there wasn't a good, Pythonic
solution. The lack of a syntax-extension facility in Python meant
everyone had to wait until iterators were finished.
But today there *are* a few syntax extension facilities in
Python, notably descriptors, upon which Python's object system is
based.
And other, more bizarre syntax extensions have been perpetrated.
mx.TextTools uses Python tuples to write a completely different
programming language.
> A prime example of this is how CLOS, the Common Lisp Object
> System was implemented completely as a loadable library (with
> the help of many macros) into Common Lisp, which was not an OO
> language prior to the adoption of CLOS.
Is there a second example? ;)
Seriously, maybe Python looks like 'blub' (thanks, Paul Graham),
to the skilled Lisp user, but it makes a lot of other languages
look like 'blub', too, including, sometimes, Lisp: Lisp has to
'blub' generators.
--
Neil Cerutti
--
http://mail.python.org/mailman/listinfo/python-list
