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Newsgroups: comp.lang.ada
Date: Thu, 3 Jan 2019 13:45:32 -0800 (PST)
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Subject: Re: Ada grammar rules for names too permissive?
From: Stephen Leake <stephen_leake@stephe-leake.org>
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Xref: reader01.eternal-september.org comp.lang.ada:55179
Date: 2019-01-03T13:45:32-08:00
List-Id: <comp.lang.ada>

On Wednesday, January 2, 2019 at 12:47:22 PM UTC-8, Dmitry A. Kazakov wrote=
:
> On 2019-01-02 20:21, Stephen Leake wrote:
> > On Tuesday, January 1, 2019 at 12:42:36 PM UTC-8, Dmitry A. Kazakov wro=
te:
> >> On 2019-01-01 20:49, Stephen Leake wrote:
> >>> On Tuesday, January 1, 2019 at 12:44:17 AM UTC-8, Dmitry A. Kazakov w=
rote:
> >>>> The grammar as written is never the one actually used for whatever
> >>>> purpose other than explanation or, maybe, validation. An extreme cas=
e
> >>>> illustrating why, is source code coloring,
> >>>
> >>> On the contrary, Emacs Ada mode source code coloring uses a generated=
 parser for the Ada language, with only minimal changes from Annex P.
> >>
> >> In which case it should not work with syntactically incorrect programs=
.
> >=20
> > No, it has error correction to deal with that.
>=20
> Ada grammar contains no correction productions.

True for LRM Annex P, and also for Emacs ada.wy, but irrelevant. For LR par=
sers, there are error correction algorithms that do not require modifying t=
he grammar. Emacs ada-mode uses the McKenzie algorithm (1); exploration of =
the parse table near the error location, combined with the redundancy of th=
e Ada language (especially named blocks).

One of these days I'll have to write a paper on it ...

Meanwhile, it works quite nicely for me, and I'm waiting to hear from more =
people on how it works for them (a few positive responses so far, no negati=
ve).

(1) McKenzie, Bruce J., Yeatman, Corey, and De Vere,
    Lorraine. Error repair in shift reduce parsers. ACM Trans. Prog.
    Lang. Syst., 17(4):672-689, July 1995.
 =20