RE: Read and "illegal" characters

[Michael Greenwald <Greenwald@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: Tue, 30 Aug 88 16:37 EDT
    From: "Steve Bacher (Batchman)" <SEB1525@draper.com>

    Yes, (a) is what I meant - the syntactic property of the character,
    not the attribute used in scanning atom names.

Then I believe that you are in luck.  

To recap:

There are no standard characters that are syntactically "illegal",
therefore no characters that *must* behave differently between single
and multiple escapes.

There is no CL sanctified way to set the syntax of a character, only to
copy the syntax.

Further, I believe it is legal for you, as a language implementor, to
define the syntax of a character. So you are free to ensure that in your
implementation, no characters have an "illegal syntactic type".
Instead, define characters you want to outlaw as "constituents" with just
the "illegal" attribute.  There is now no way to create the problem
characters.

As I said before, this finesses the practical problem, but does not
solve the academic problem.  My personal hope is that the distinction
between single and multiple-escapes is unintentional.  The 2 paragraphs
on pg 338 seems to support this:

  "As a rule, a @i(single escape) character never stands for itself but
  always serves to cause the following character to be treated as a simple
  alphabetic character.  A @i(single escape) character can be included in
  a token only if preceded by another @i(single escape) character.
  
   A @i(multiple escape) character also never stands for itself.  The
  characters between  a pair of @i(multiple escape) characteres are all
  treated as simple alphabetic characrters, except that @i(single escape)
  and @i(multiple escape) characters must nevertheless be preceded by a
  @i(single escape) character to be included."
  
Perhaps the cleanup committee has dealt with this issue already.  I
don't know.