RFC 226 (v2) Selective interpolation in single quotish context.

This and other RFCs are available on the web at
  http://dev.perl.org/rfc/

=head1 TITLE

Selective interpolation in single quotish context.

=head1 VERSION

  Maintainer: Brad Hughes <[email protected]>
  Date: Sep. 14, 2000
  Last Modified: Sep. 14, 2000
  Mailing List: [email protected]
  Number: 226
  Version: 2
  Status: Developing

=head1 ABSTRACT

Perl6 should allow scalars and arrays to be tagged such that they are
interpolated in single quotish context.

=head1 DESCRIPTION

Single quotish context, such as C<q{}>, C<''>, and specified here-docs,
is especially useful for large blocks of text which may contain
the C<$> and C<@> characters.  Frequently, however, interpolation within
that large block of text is desired.  This RFC proposes that in single
quotish context scalars and arrays may be tagged to be interpolated.

As an example, on the VMS operating system the C<$> runs rampant
through VMS namespaces, not to mention that each line of VMS' equivalent
of a Unix shell script (called a .com file) starts with a C<$>, and execution
of VMS .com files is invoked with a C<@>, resulting in backslashitis:

        print F <<END;
        \$!
        \$! execute a.com, copy and purge
        \$!
        \$ \@sys\$login:a.com
        \$ copy $filename sys\$login:*.*
        \$ purge sys\$login:$filename
        \$!
        \$ exit
        END

With this proposal, the scalar C<$filename> can be tagged to be interpolated
by the C<\I...\E> pair and the double quotish context replaced by single
quotish context resulting in the following:

        print F <<'END';
        $!
        $! execute a.com, copy and purge
        $!
        $ @sys$login:a.com
        $ copy \I$filename\E sys$login:*.*
        $ purge sys$login:\I$filename\E
        $!
        $ exit
        END

An array can be similarly tagged.  Would C<\I&subr\E> call subr?.

=head1 IMPLEMENTATION

This wouldn't seem a difficult change to make.
  
=head1 REFERENCES

Originally suggested in a different form by Jarkko Hietaniemi <[email protected]> in
<archive address to follow>, and seconded by Mark-Jason Dominus
<[email protected]> in <archive address to follow>.
Version 2 tag pair suggested by Damian Conway in <...>.