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From: Markus Triska <triska@gmx.at>
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Subject: Re: Finding Unused Identifiers
Date: Thu, 02 Mar 2006 18:18:05 +0100
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Hi!

B. T. Raven wrote:

 > by "unused" do you mean something other than unbound?

I took it to mean "(at least) one write access (set, let, ...), and no 
read access".

> Why can't the file be loaded

Consider:

(let ((a 0))
   (complicated-function) ; not involving a
   (print a))

If "complicated-function" halts, a is (subsequently) used. If it 
doesn't, a remains unused (the "print" part is never reached). Since 
whether a Lisp function halts is undecidable, there's no algorithm that 
always both terminates and correctly identifies all such identifiers in 
arbitrary programs.

All the best,
Markus.