Re: A simpler definition of the Bidi Algorithm

From: Asmus Freytag (
Date: Fri Sep 10 2010 - 19:00:21 CDT

  • Next message: Khaled Hosny: "Re: A simpler definition of the Bidi Algorithm"

      The first discussions that lead to the current formulation of the bidi
    algorithm easily go back 20 years by now. There's some value in not
    re-stating a specification - even if a new formulation could be found to
    be 100% equivalent. That value lies in the fact that any reader can
    tell, by simple inspection, that the specification hasn't changed, and
    that implementations that claim conformance to earlier versions of the
    specification are indeed still conformant to later versions.

    This point is particularly important for the bidi algorithm, because of
    it's mandatory nature and the fact that it gets re-issued with a new
    version number every time that the underlying Unicode standard gets a
    new version (because of new characters added, etc).

    That does not preclude other, equivalent formulations of the algorithm,
    whether in text books or, perhaps, as technical Note. But the burden is
    on the creators of these other formulations to show that their
    supposedly easier or more didactic presentation is indeed equivalent.

    Having said that, there are already two other formulations of the
    algorithm that are proven to be equivalent to each other (and have not
    proven to deviate from the written algorithm). I'm referring of course
    to the C++ (
    and Java reference implementations.


    PS: Personally, I don't find the presentation in terms of the regular
    expressions any more intuitive than the original.

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