[Python-Dev] A Hygienic Macro System in Python? (original) (raw)

Paul Prescod paul@prescod.net
Mon, 18 Mar 2002 13:41:50 -0800

Tom Emerson wrote:

... Sure, here's one from Dylan, that provides a useful bit of syntactic sugar that makes some code easier to read: define macro unless { unless (?test:expression) ?:body end } => { if (~ ?test) ?body end }

I think that's a poor example. If Guido wanted to read Python code with unless in it he would just add it to the language. If you want to make a case for macros then I would suggest you use an example some obscure domain where Guido doesn't know enough to recognize that Python is already good enough as it is. ;) Niel S is on the right track describing workarounds he's had to do for "eval" and import hooks. In that case the need was severe enough that they decided to make a Python-like language even though it was quite difficult. So they've proven that they needed something like macros enough to implement something like them themselves. Macros' cost in compile-time is high enough that IMO you should only use them when you really need them. And I would want them to be very glaring...as in:

macro unless(has_foo(bar)): do_something()

I want to really be clear when I read code of what's built-in and what's extension stuff.

Paul Prescod