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=head1 TITLE
Alternative lists and quoting of things
=head1 VERSION
Maintainer: Richard Proctor [EMAIL PROTECTED]
Date: 27 Aug 2000
Last Modified: 15 Sep 2000
Mailing List: [EMAIL PROTECTED]
Number: 166
Version: 2
Status: Developing
=head1 ABSTRACT
Expand Alternate Lists from Arrays and Quote the contents of things
inside regexes.
=head1 DESCRIPTION
These are a couple of constructs to make it easy to build up regexes
from other things.
=head2 Alternative Lists from arrays
The basic idea is to expand an array as a list of alternatives. There
are two possible syntaxs (?@foo) and just plain @foo. @foo might just have
existing uses (just), therefore I prefer the (?@foo) syntax.
(?@foo) is just syntactic sugar for (?:(??{ join('|',@foo) })) A bracketed
list of alternatives.
=head2 Quoting the contents of things
If a regex uses $foo or @bar there are problems if the content of
the variables contain special characters. What is needed is a way
of \Quoting the content of scalars $foo or arrays (?@foo).
Suggested syntax:
(?Q$foo) Quotes the contents of the scalar $foo - equivalent to
(??{ quotemeta $foo }).
(?Q@foo) Quotes each item in a list (as above) this is equivalent to
(?:(??{ join ('|', map quotemeta, @foo)})).
In this syntax the Q is used as it represents a more inteligent \Quot\E.
=head2 Comments
Hugo:
(?@foo) and (?Q@foo) are both things I've wanted before now. I'm
not sure if this is the right syntax, particularly if RFC 112 is
adopted: it would be confusing to have (?@foo) to have so
different a meaning from (?$foo=...), and even more so if the
latter is ever extended to allow (?@foo=...).
I see no reason that implementation should cause any problems
since this is purely a regexp-compile time issue.
Me: I cant see any reasonable meaning to (?@foo=...) this seams an appropriate
syntax, but I am open for others to be suggested.
=head1 CHANGES
RFC 166, v1 was entitled "Additions to regexes".
V1 of this RFC had three ideas, one has been dropped, the other is now part
of RFC 198.
V2 Expands the list expansion and quoting with quoting of scalars and
Implemention issues.
=head1 MIGRATION
As (?@foo) and (?Q...) these are additions with out any compatibility issues.
The option of just @foo for list exansion, might represent a small problem if
people already use the construct.
=head1 IMPLENTATION
Both of these are changes are regex compile time issues.
Generating lists from arrays almost works by localising $" as '|' for the
regex and just using @foo.
MJD has demonstrated implementing (?@foo) as (?\@foo) by means of an overload
of regexes, this slight change was necessary because of the expansion of
@foo - see below.
Both of these changes are currently affected by the expansion of variables in
the regex before the regex compiler gets to work on the regex. This problem also
affects several other RFCs. The expansion of variables in regexes needs
for these (and other RFCs) to be driven from within the regex compiler so
that the regex can expand as and where appropriate. Changing this should not
affect any existing behaviour.
=head1 REFERENCES
RFC 198: Boolean Regexes
