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From: Natacha Kerensikova <lithiumcat@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: S-expression I/O in Ada
Date: Thu, 12 Aug 2010 13:11:48 -0700 (PDT)
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On Aug 12, 8:55=A0pm, Jeffrey Carter
<spam.jrcarter....@spam.not.acm.org> wrote:
> The example was something like
>
> (TCP-something (host abc) (port 42) )
>
> So I think the grammar is
>
> S-expression =3D '(' Element {' ' Element} ')'
>
> Element =3D Atom | S-expression

Actually a S-expression list can be empty, and a S-expression can be a
single atom, or a list of atom, without parentheses.

The grammar would be more something like:

SP =3D TAB | SPACE | CR | LF  -- whitespace

S-expression =3D SP* (Atom | List)* SP*

List =3D '(' S-expression* ')'

Atom =3D Token-Atom | Quoted-String-Atom | Hexadecimal-Atom | Base64-
Atom | Verbatim-Atom

And the rest I'm not sure can be described by a grammar (especially
verbatim encoded atoms), and that's without entering into details like
brace encoding or display hints (which sucks anyway). The whitespace
being optional because generally atoms don't need separators, token-
encoded atoms being the exception (unfortunately all atoms from my
example are token-encoded).


Hoping it helps,
Natacha