[Compiler-sig] Re: example checkers based on compiler package

[Moshe Zadka]

On Mon, 6 Mar 2000, Jeremy Hylton wrote:

> I think these kinds of warnings are useful, and I'd like to see a more
> general framework for them built are Python abstract syntax originally
> from P2C.  Ideally, they would be available as command line tools and
> integrated into GUIs like IDLE in some useful way.

Yes! Guido already suggested we have a standard API to them. One thing
I suggested was that the abstract API include not only the input (one form
or another of an AST), but the output: so IDE's wouldn't have to parse
strings, but get a warning class. Something like a:

An output of a warning can be a subclass of GeneralWarning, and should
implemented the following methods:

	1. line-no() -- returns an integer
	2. columns() -- returns either a pair of integers, or None
        3. message() -- returns a string containing a message
	4. __str__() -- comes for free if inheriting GeneralWarning,
	                and formats the warning message.

> I've included a couple of quick examples I coded up last night based
> on the compiler package (recently re-factored) that is resident in
> python/nondist/src/Compiler.  The analysis on the one that checks for
> name errors is a bit of a mess, but the overall structure seems right.

One thing I had trouble with is that in my implementation of selfnanny,
I used Python's stack for recursion while you used an explicit stack.
It's probably because of the visitor pattern, which is just another
argument for co-routines and generators.

> I'm hoping to collect a few more examples of checkers and generalize
> from them to develop a framework for checking for errors and reporting
> them.

Cool! 
Brainstorming: what kind of warnings would people find useful? In
selfnanny, I wanted to include checking for assigment to self, and
checking for "possible use before definition of local variables" sounds
good. Another check could be a CP4E "checking that no two identifiers
differ only by case". I might code up a few if I have the time...

What I'd really want (but it sounds really hard) is a framework for
partial ASTs: warning people as they write code.

--
Moshe Zadka <mzadka@geocities.com>. 
http://www.oreilly.com/news/prescod_0300.html