my @a = ( .. some extremely huge array .. );
my @want = ( .. some array of things I want to find )

my $index_a = make_indexfinder(\a);

foreach ( @want ) {
    print $index_a->($want), "\n";
}

sub make_indexfinder {
    my ($arrayref) = @_;

    my %value_table = ();
    my $last_index = 0;

    return sub {
        my ($quarry) = @_;

        exists $value_table{$quarry} and return $value_table{$quarry};

        for ($last_index .. $#$arrayref) {
            ($quarry eq $arrayref->[$_]) and do {
                $last_index = $_;
                $value_table{ $quarry } = $_;
                return $_;
            };
            $value_table{ $arrayref->[$_] } = $_;
        }
        return undef;
    };
}