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

19 Mar 2002 12:18:59 +0100

Greg Ewing <greg@cosc.canterbury.ac.nz> writes:
> I've been trying to think of a Pythonic syntax for passing
> code blocks to procedures. The best thing I've come up with
> so far is something like
>> lock.do:
> something()

Another approach, which I've been thinking about for quite some time
now:
 under <expr>:
 something()
where <expr> evaluates to a controller object that implements a certain
interface. The code above would be more or less equivalent to this (the
__controller__ variable would only exist in the interpreter somewhere):
 __controller__ = <expr>
 while __controller__.should_run():
 try:
 try:
 __controller__.start()
 something(x)
 __controller__.end()
 except:
 __controller__.exception()
 finally:
 __controller__.exit()
This sort of thing would make some parts of Sketch a bit easier. I've
quite a few places with code like:
 doc.BeginTransaction()
 try:
 try:
 something()
 except:
 # an error occurred part way through. make sure everything
 # is reverted (sort of a rollback)
 doc.AbortTransaction()
 finally:
 doc.EndTransaction()
This could be replaced by:
 under doc.Transaction():
 something()
Bernhard
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