#!/usr/bin/env perl -l

use strict;
use warnings;

my @matrix = (
    [qw{A B C}],
    [qw{D E F}],
    [qw{G H I}],
    [qw{J K L},
        [
            [qw{M N O P Q}, [qw{R S T}], qw{U V W X Y Z}]
        ]
    ],
);
my %dict = (
    a => [0, 0],
    b => [0, 1],
    e => [1, 1],
    g => [2, 0],
    i => [2, 2],
    p => [3, 3, 0, 3],
    s => [3, 3, 0, 5, 1],
);

for (qw{a b e g i p s}) {
    print "$_ => ", get_element(\@matrix, $dict{$_});
}

sub get_element {
    my ($matrix, $coords) = @_; 

    my $element = $matrix->[shift @$coords];
    @$coords ? get_element($element, $coords) : $element;
}