Re: Perl source filter question

[Mike Cramer <cramer@webkist.com>]

Mark Dominus wrote:
> Eric Roode said it was exceptionally difficult to solve this, but that
> wasn't strong enough.  It is impossible.  There is a mathematical
> proof that there's no solution; it's called "Rice's theorem".  But the
> content of the theorem is completely unsurprising: there are no
> shortcuts to computation; if you want to know the result of computing
> something, you actually have to compute it.

Yes...this is obviously true, but luckily the problem I'm trying to 
solve is much smaller.

> There's a big technical difficulty with your question, since from
> Perl's point of view, built-in functions like 'print' and 'sleep' are
> not the same kind of thing as used-defined functions like 'CGI::new'
> and 'CGI::header'.  And, even worse, 'use' and 'my' are not functions
> at all.  It's not even clear to me why you want the output to include
> 'use' and 'my', but not '->' (which is known internally inside Perl as
> 'pp_method') or '==' or 'qq' or '='.

Plain and simple ignorance...I was basically thinking of functions as 
anything in "Functions" chapter of Programming Perl, plus anything 
imported from another module. As you might have guessed, I'm not 
*really* interested in 'use' or 'my'.

> The B:: modules can't see at compile time that the code will run the
> 'sleep' operator at run time.  The only way to find out what a program
> will do if you run it, is to actually run it.  If there were a
> shortcut to computation, then we wouldn't actually need to compute,
> and then we'd all be out of a job.
>
> I hope this was more helpful than frustrating.  It would help to know
> more about what you are actually trying to accomplish and why.

I might as well come clean. It's very simple: someone I work with wrote 
some Apache::Registry scripts that use the one-arg form of "select" to 
write out files on the webserver, but neglected to restore the 
originally selected filehandle. So the immediate question was, "What 
other scripts are calling select?"

But I figured, why not try to find something a little more generic? 
Basically, something that can tell me which scripts contained references 
to, say, Digest::MD5::md5hash? I understand that eval is going to be 
impossible without actually running the program, and that's fine. I 
picture it as more of a basic dependency analysis -- although as you 
pointed out, internal functions wouldn't be "dependencies" in the same 
way that functions from an external module are. And, ultimately, with 
AUTOLOAD and everything, even the existance of method calls might not be 
verifiable until runtime. I don't need to know what *will* be called, 
just what *might* be called.

--
Mike Cramer
http://www.webkist.com/ | AIM: MikeWebkist

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