I'd probably use a tied array.

#!perl

use strict;
use warnings;
use feature 'say';
use Data::Dumper;

BEGIN {
    package Array::CaseFolded;
    
    # Perl 5.16 has 'fc' feature; older Perls can just use 'lc'.
    use if $] >= 5.016, feature => 'fc';
    BEGIN { $] < 5.016 and eval 'sub fc ($) { lc $_[0] }' };
    
    # Copied from Tie::StdArray.
    # Altered STORE, PUSH, UNSHIFT, and SPLICE.
    sub TIEARRAY  { bless [], $_[0] }
    sub DESTROY   { }
    sub EXTEND    { }
    sub FETCHSIZE { scalar @{$_[0]} }
    sub STORESIZE { $#{$_[0]} = $_[1]-1 }
    sub STORE     { $_[0]->[$_[1]] = fc $_[2] }
    sub FETCH     { $_[0]->[$_[1]] }
    sub CLEAR     { @{$_[0]} = () }
    sub POP       { pop( @{$_[0]} ) }
    sub PUSH      { my $o = shift; push( @$o, map fc $_, @_ ) }
    sub SHIFT     { shift( @{$_[0]} ) }
    sub UNSHIFT   { my $o = shift; unshift( @$o, map fc $_, @_ ) }
    sub EXISTS    { exists $_[0]->[$_[1]] }
    sub DELETE    { delete $_[0]->[$_[1]] }
    sub SPLICE {
        my $ob  = shift;
        my $sz  = $ob->FETCHSIZE;
        my $off = @_ ? shift : 0;
        $off   += $sz if $off < 0;
        my $len = @_ ? shift : $sz-$off;
        return splice( @$ob, $off, $len, map fc($_), @_ );
    }
    
    # Utility functions
    sub contains {
        my ( $arr, $value ) = ( shift, fc shift );
        !!grep $value eq $_, @$arr;
    }
    sub after {
        my ( $arr, $value ) = ( shift, fc shift );
        my $found = -1;
        for my $i ( 0 .. $#$arr ) {
            next unless $arr->[$i] eq $value;
            $found = $i;
            last;
        }
        $found >= 0 and $found < $#$arr and return $arr->[ $found + 1 
+];
        return undef;
    }
};

tie my @arr, 'Array::CaseFolded';

@arr = qw( Foo BAR baz );

print Dumper(\@arr);

say tied(@arr)->contains( 'Bar' );

say tied(@arr)->after( 'Bar' );
[download]

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