Re: Unquoted special characters in regexps

[Luc Teirlinck]

>From my previous reply:

   As Andreas already pointed out, there is _no_ way to determine whether
   either a `]' _or_ a `\\]' has to be taken literally or closes a
   character alternative without parsing the regexp forward from the start.

Well, _in certain cases_, you might be able to determine it sooner by
parsing backward from the `]'.  If you see a `]' or "\\]" you know it
has to be taken literally.  (Note: the "\\" are irrelevant to the
question again.)  But then you do not know whether that earlier `]' or
"\\]" has to be taken literally, without keeping going.  If you see an
unquoted [, you know that the `]' closes a character alternative, but
you still do not know whether that `[' is opening that character
alternative or has to be taken literally, as in "[asd[fgh]".  If you
encounter another `[' next you know that either that one opens your
character alternative _or_ that the regexp was very poorly written.

But there definitely are many cases where you would have to parse back
all the way to the beginning.

Sincerely,

Luc.