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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: S-expression I/O in Ada
Date: Thu, 12 Aug 2010 21:59:44 +0200
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Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org> writes:
> On 08/12/2010 12:53 AM, Ludovic Brenta wrote:
>> * the parser also supports lists of the form (a b c) (more than 2
>> elements) and properly translates them to (a (b c)).  The Append()
>> procedure that does this is also public and available to clients.
>
> The example was something like
>
> (TCP-something (host abc) (port 42) )
>
> So I think the grammar is
>
> S-expression = '(' Element {' ' Element} ')'
>
> Element = Atom | S-expression
> 
> and you've implemented something slightly different.

If I understand your quasi-BNF correctly, an S-Expression in your
grammar can have only one or two, but not three elements.  This
contradicts the "(TCP-something (host abc) (port 42) )" example, which
has three elements.

In reality, an S-Expression (a "cons pair" in Lisp parlance) can indeed
not have three elements; the notation (a b c) is, really, shorthand for
(a (b c)); I was keen to implement that in my parser.  See

http://en.wikipedia.org/wiki/S-expression#Definition

-- 
Ludovic Brenta.