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Opinions wanted: What should (.list pmacro-name 42) do?
- From: Doug Evans <dje at sebabeach dot org>
- To: cgen at sourceware dot org
- Date: Thu, 20 Aug 2009 10:30:32 -0700
- Subject: Opinions wanted: What should (.list pmacro-name 42) do?
Hi.
What should the output of
(define-pmacro (foo a) (add a 1))
(.list foo 42)
be?
Currently the result is (<pmacro> 42)
where <pmacro> is the pmacro object for "foo".
It's not ideal because it means that a pmacro object "escapes"
pmacro-processing and can be seen by, for example, rtl compilation.
However, it's not that unexpected. The user asked for a list containing
two objects, the pmacro and 42.
This is akin to saying (list + 42) in Scheme.
We *could* have the pmacro evaluator re-examine the result and if it
sees (<pmacro> mumble) then re-expand it. That's what we do for symbols
today (i.e. if the result of pmacro-expansion is a symbol that names a
pmacro, we re-evaluate it), but that has problems, e.g.
http://sourceware.org/ml/cgen/2009-q3/msg00052.html
and I'm leaning toward removing that behavior.
It's not clear to me what The Right Thing to do is.
Opinions?