getval.php

<?
function findKey($arr, $key) {
	return $arr[$key];
}
function superFunction($arr, $path) {
	if (is_array($arr)) {
		$path_str = explode('.', $path);
		foreach ($path_str as $key) {
			$arr = findKey($arr, $key);
		}
		return $arr;
	}
}

$arr = [
	'list' => [
		'first'  => [
			'val1' => 'one',
			'val2' => 'two',
		],
		'second' => [
			'val11' => 'one1',
			'val21' => 'two2',
		],
	],
];

echo superFunction($arr, 'list.first.val1'); // one
echo superFunction($arr, 'list.second.val21'); // two2

function findKey ($arr, $key)                                                  
{                                                                                
    return $arr[$key];                                                           
}                                                                                
function superFunction ($arr, $path)                                             
{                                                                                
    if (is_array($arr))                                                          
    {                                                                            
        $path_str = explode('.', $path);                                         
        foreach ($path_str as $key)                                              
        {                                                                        
            $arr = findKey($arr, $key);                                          
        }                                                                        
        return $arr;                                                             
    }                                                                            
}                                                                                

$arr = [                                                                         
    'list' => [                                                                  
        'first' => [                                                             
            'val1' => 'one',                                                     
            'val2' => 'two',                                                     
        ],                                                                       
        'second' => [                                                            
            'val11' => 'one1',                                                   
            'val21' => 'two2',                                                   
        ],                                                                       
    ],                                                                                                                                                                                
];                                                                               

echo superFunction($arr, 'list.first.val1'); // one                              
echo superFunction($arr, 'list.second.val21'); // two2                           

Cпасибо!
Обновил.