Reserve #! for read directives

[cowan]

From Denis Washington:

Reading chapter 2 of the third draft, I was thinking: now that we have #!fold-case and #!no-fold-case and other directives might follow in WG2, wouldn't it be appropriate for section 2.3 (Other notations) to define #! as generally introducing a "read directive"? That would encourage implementations to use the same syntax for their own directives, which helps portability (an implementation could just ignore unknown directives which might just be used by another for optimization purposes). Just an idea.

[cowan]

Andy Wingo notes:

FWIW, this use is incompatible with scsh-style block comments. Specific tokens can always be special-cased. But treating #!TOKEN as a general read-directive is incompatible with this style of comment.

Guile also has these comments, and they are pervasive, unfortunately.

John Cowan pointed out that a comment-start directive is a kind of read directive.

[cowan]

WG1 rejected this proposal.