[pypy-dev] Questions about the C core
andrew at indranet.co.nz
Sun Jan 12 02:32:54 CET 2003
Has anyone thought about features that Python does not have that should be
in Minimal? My first candidate would be (ducks) macros, since that could
drastically simplify constructing core Python features. I have some
thoughts on pythonic ways to do that which I need to write up. Basically,
if we use the parser module rather than a C parser, it gets to be fairly
So, what would a pythonic macro look like?
The nearest match presently is a metaclass, but that only gets the class
definition *after* compilation, which means that although we can modify the
code at that point (even to the extent of retreiving the source, changing
it and recompiling), it had to compile in the first place, so we can't add
Therefore a Pythonic macro should be:
A class which adds it's grammar (probably fairly constrained; limited to
new keywords, perhaps) to the parser at parse time, by setting or appending
to a magic attribute (__grammar__ perhaps).
Then the macro provides code which is called with the parse trees resulting
from that grammar, modifies them, and returns the parse tree that will
actually be compiled. If you want to evaluate some bits at compile time,
do that explicitly in the macro (opposite way around to lisp, where you
have complicated rules).
It may be necessary to provide a quote: keyword and quote() (or noeval()?
should the names be different?) builtin that quote a block or an expression
to prevent compile-time evaluation by macros.
It looks like a metaclass.
It can be inherited from to use the macro in new classes (hence __grammar__
should be appended to rather than just set).
If the kinds of grammar rules that can be added are constrained just right,
editors won't mess up the indentation and code using macros will still look
If, however, we can use unconstrained grammar mods in the core, then we can
do things like build dictionaries inline.
Hmm, must go now, I was dreaming up an example, but I've got to go sell a
house (Hooray :-)
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