use warnings;
use strict;

#  true
x in 'v'..'z';

#  false
xx in 'v'..'z';

#  but variables aren't barewords

my $x='x';
in->$x('v'..'z');





package in;

use Data::Dump qw/pp/;
our $AUTOLOAD;

sub AUTOLOAD {
    
    (my $LHS= $AUTOLOAD) =~ s/in:://;

    #print  pp [$LHS, @_];

    my $res = grep {$LHS eq $_ } @_;

    my $not ="";
    $not =' not' unless $res;
    
    warn "$LHS$not @_";

    return $res;
}

##</code><code>##

/usr/bin/perl -w /tmp/in.pl 
x in v w x y z at /tmp/in.pl line 35.
xx not in v w x y z at /tmp/in.pl line 35.
x in v w x y z at /tmp/in.pl line 35.

Compilation finished at Wed Aug 26 13:51:16