'tye2' => sub {
        my $f = ord($str_a);
        for my $str_b ( @list ) {
            next if $f != ord( $str_b );
            expensive_function ( $str_a, $str_b );
        }
    },

##</code><code>##

        Rate   hb1   hb2  L~R3   BUk  L~R2  dlrm   L~R  tye1 kvale  tye2
hb1   46.5/s    --  -35%  -35%  -38%  -60%  -62%  -70%  -73%  -73%  -74%
hb2   71.4/s   53%    --   -0%   -6%  -38%  -42%  -54%  -59%  -59%  -61%
L~R3  71.4/s   53%    0%    --   -6%  -38%  -42%  -54%  -59%  -59%  -61%
BUk   75.7/s   63%    6%    6%    --  -35%  -39%  -51%  -56%  -56%  -58%
L~R2   116/s  149%   62%   62%   53%    --   -6%  -25%  -33%  -33%  -36%
dlrm   124/s  166%   73%   73%   63%    7%    --  -20%  -28%  -29%  -32%
L~R    155/s  233%  117%  117%  105%   34%   25%    --  -10%  -11%  -14%
tye1   172/s  270%  141%  141%  128%   48%   39%   11%    --   -1%   -5%
kvale  174/s  274%  143%  143%  130%   50%   41%   12%    1%    --   -4%
tye2   181/s  289%  154%  154%  139%   56%   46%   17%    5%    4%    --