RFC 320 (v1) Allow grouping of -X file tests and add C<filetest> builtin

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=head1 TITLE

Allow grouping of -X file tests and add C<filetest> builtin

=head1 VERSION

  Maintainer: Nathan Wiger <[email protected]>
  Date: 25 Sep 2000
  Mailing List: [email protected]
  Number: 
  320
  Status: Developing

=head1 ABSTRACT

Currently, file tests cannot be grouped, resulting in very long
expressions when one wants to check to make sure some thing is a
readable, writeable, executable directory:

   if ( -d $file && -r $file && -w $file && -x $file ) { ... }

It would be really nice if these could be grouped instead:

   if ( -drwx $file ) { ... }

Notice how much easier this is to read and write.

=head1 DESCRIPTION

=head2 File Test Grouping

See above. Multiple file tests, when grouped, should be ANDed together.
This RFC does not propose a way to OR them, since usage like this:

   if ( -d $file || -r $file || -w $file || -x $file ) { ... }

Is highly uncommon, to say the least.

Notice this has the nice side effect of eliminating the need for C<_> in
many cases, since this:

   if ( -d $file && -r _ && -w _ && -x _ ) { ... }

Can simply be written as a single grouped file test, as shown above. If
you need to check for more complex logic, you still have to do that
separately:

   if ( -drwx $file and ! -h $file )  { ... }

This is the simplest and also probably the clearest way to implement
this.

=head2 New C<filetest> Builtin

This RFC also proposes a new C<filetest> builtin that is actually what
is used for these tests. The C<-[a-zA-Z]+> form is simply a shortcut to
this builtin, just like <> is a shortcut to C<readline>. So:

   if ( -rwdx $file ) { ... }

Is really just a shortcut to the C<filetest> builtin:

   if ( filetest $file, 'rwdx' ) { ... }

Either form could be used, depending on the user's preferences (just
like C<readline>).

=head1 IMPLEMENTATION

This would involve making C<-[a-zA-Z]+> a special token in all contexts,
serving as a shortcut for the C<filetest> builtin.

=head1 MIGRATION

There is a subtle trap if you are negating subroutines:

   $result = -drwx $file;

And expect this to be parsed like this:

   $result = - &drwx($file);

However, usage such as this is exceedingly unlikely, and can simply be
resolved by the p52p6 translator looking for C<-([a-zA-Z]{2,})> and
replacing it with C<- $1>, since injecting a single space will break up
the token.

=head1 REFERENCES

This grew out of a discussion on RFC 290 between myself, John Allen,
Clayton Scott, Bart Lateur, and others