Re: build-lexical-var vs. -Wunused-variable

[Mark H Weaver <mhw@netris.org>]

Andy Wingo <wingo@pobox.com> writes:
> On Fri 17 Feb 2012 12:00, ludo@gnu.org (Ludovic Courtès) writes:
>
>> Commit f9685f437312ea790981373ddc375b2a26ba9c4f changes
>> ‘build-lexical-var’ like this:
>>
>>      (define-syntax-rule (build-lexical-var src id)
>> -      (gensym (string-append (symbol->string id) " ")))
>> +      (gensym (string-append (symbol->string id) "-")))
>>
>> This breaks a heuristic used in the ‘unused-variable’ pass, which is
>> that identifiers containing white space are likely introduced by a macro
>> and can be ignored in unused-variable reports (see ‘gensym?’ in
>> ‘tree-il/analyze.scm’).
>>
>> OK to change it back?
>
> How about we use `$' instead?  I understand that's how Chez does it.
> I'd really rather something that is printable without the #{#} syntax.

Now that we have a (pending) patch to avoid printing gensyms to
psyntax-pp.scm, does that change your opinion on this?  I tend to agree
with Ludovic here.  In general, any character that doesn't require the
#{}# syntax is likely to be used by some programs in their identifier
names.  It would be a shame if we disabled unused-variable warnings for
variables whose name contains a '$', or any other standard identifier
character for that matter.

     Thanks,
       Mark