[Python-ideas] Macros for Python

[Haoyi Li]

I thought this may be of interest to some people on this list, even if not
strictly an "idea".

I'm working on MacroPy <https://github.com/lihaoyi/macropy>, a little
pure-python library that allows user-defined AST rewrites as part of the
import process (using PEP 302). In short, it makes mucking around with
Python's semantics so easy as to be almost trivial: you write a function
that takes an AST and returns an AST, register it as a macro, and you're
off to the races. To give a sense of it, I just finished implementing
Scala/Groovy style anonymous lambdas:

map(f%(_ + 1), [1, 2, 3])#[2, 3, 4]
reduce(f%(_ + _), [1, 2, 3])#6

...which took about half an hour and 30 lines of code, start to finish.
We're currently working on implementing destructuring-pattern-matching on
objects (i.e. like in Haskell/Scala) and a clone of .NET's LINQ to SQL.

It's still very much a work in progress, but we have a list of pretty cool
macros already done, which shows off what you can do with it. If anyone
else was thinking about messing around with the semantics of the Python
language but was too scared to jump into the CPython internals, this offers
a somewhat easier path.

Hope this was interesting to somebody!
-Haoyi
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