[armedbear-devel] Making tags (in tagbody) and block names unique
ehuels at gmail.com
Mon Sep 28 20:04:55 UTC 2009
On Sun, Sep 27, 2009 at 11:37 PM, Erik Huelsmann <ehuels at gmail.com> wrote:
> On IRC, we had a discussion some days ago where it was found that ABCL
> doesn't use unique tag-identifications in tagbody, leading to somewhat
> dynamically scoped tagbodies, instead of perfectly lexically scoped.
> BLOCK also uses non-unique names (think NIL), leading to the same
> issue. Both the compiler and the interpreter exhibit the problem.
Actually, to be specific: BLOCK is a compiler issue (as it turns out
BLOCK does do the right thing in the interpreter), TAGBODY is an
interpreter and compiler issue.
> Consider the following code:
> (labels ((p (b)
> (if (not b)
> (p #'(lambda () (go :foo)))
> (funcall b))
> (return-from p :bar)
> (return-from p :foo))))
> (p nil))
Or, for BLOCK, consider the following:
(labels ((p (b)
(if (not b)
(p #'(lambda () (return :foo)))
(return-from p :bar))))
> It should return :foo, but return :bar on ABCL's interpreter instead.
> (The fact that the compiler works, means there's probably a bug in it
> somewhere, because there's no explanation why it would.)
The BLOCK code returns :BAR on 0.16.0.
> I'm now thinking of ways to make the tags/blocknames unique. The one
> way I could come up with for the interpreter is this:
[ snip ]
I committed a change for BLOCK which replaces a static symbol with the
content of a closure variable. This variable is set up upon entry of
the block form and contains a unique identifier by allocating a
specific LispObject, but *only* if the block contains non-local
I'm thinking of the right way to do the same with TAGBODY.
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