GNU bug report logs - #20087
'gensym' is not guaranteed to return a fresh symbol

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Package: guile;

Reported by: ludo <at> gnu.org (Ludovic Courtès)

Date: Wed, 11 Mar 2015 17:16:02 UTC

Severity: normal

Done: Andy Wingo <wingo <at> pobox.com>

Bug is archived. No further changes may be made.

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From: ludo <at> gnu.org (Ludovic Courtès)
To: 20087 <at> debbugs.gnu.org
Subject: bug#20087: 'gensym' is not guaranteed to return a fresh symbol
Date: Wed, 11 Mar 2015 18:15:02 +0100

‘gensym’ returns interned symbols, but the algorithm to determine the
new symbol is simplistic and predictable.

Thus, one can arrange to produce a symbol before ‘gensym’ does, leading
‘gensym’ to return a symbol that’s not fresh (in terms of ‘eq?’), as is
the case with the second call to ‘gensym’ here:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (gensym "x")
$1 = x379
scheme@(guile-user)> 'x405
$2 = x405
scheme@(guile-user)> (gensym "x")
$3 = x405
--8<---------------cut here---------------end--------------->8---

Should we worry about it?  I think it may have hard to anticipate
security implications.

Ludo’.
This bug report was last modified 9 years and 30 days ago.

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