Re: [Scheme-reports] #\@ starting an identifiers

On Fri, Oct 11, 2013 at 1:47 AM, John Cowan <cowan@x> wrote:

Michael Montague scripsit:

> The lexical rules given in 7.1.1 do not allow #\@ as the initial
> character of an identifier. One of the quasiquote examples and the note
> above, assume that identifiers can start with #\@.
>
> I assume that the lexical rules are correct and #\@ is not allowed as an
> initial character of an identifier.

It is not allowed in the standard language. However, it is a legitimate
implementation extension to the lexical syntax, in which case the note
in 4.2.8 applies.

Actually, this was ticket #12 in the second ballot, which

sides with the prose in section 2.1:

An identifier is any sequence of letters, digits, and "extended

identifier characters" provided that it does not have a prefix

which is a valid number.

The formal syntax was updated partially to allow identifiers

beginning with - or +, but <special initial> was not updated

to include additional ASCII characters. I believe @ is the

only character missing from that list.

@ in particular is important because it makes the SSAX

syntax retroactively valid.

Alex