php function help?

Suppose I have this code

$num = $_SESSION['count'];
$_SESSION['a'][$num] = $a_letter;
$_SESSION['b'][$num] = $b_letter;
$_SESSION['c'][$num] = $c_letter;
$_SESSION['d'][$num] = $d_letter;
$_SESSION['e'][$num] = $e_letter;
$_SESSION['f'][$num] = $f_letter;



if(!exists) {

$num = $_SESSION['count'];
$_SESSION['a'][$num] = $a_letter;
$_SESSION['b'][$num] = $b_letter;
$_SESSION['c'][$num] = $c_letter;
$_SESSION['d'][$num] = $d_letter;
$_SESSION['e'][$num] = $e_letter;
$_SESSION['f'][$num] = $f_letter;
}


else {
$num = $_SESSION['count'];
$_SESSION['a'][$num] = $a_letter;
$_SESSION['b'][$num] = $b_letter;
$_SESSION['c'][$num] = $c_letter;
$_SESSION['d'][$num] = $d_letter;
$_SESSION['e'][$num] = $e_letter;
$_SESSION['f'][$num] = $f_letter;

}

Now I don't want those codes to copy paste repetitively, but instead I want to come up with a function - So I probably have to create a function in php then??


function list ()

{
$num = $_SESSION['count'];
$_SESSION['a'][$num] = $a_letter;
$_SESSION['b'][$num] = $b_letter;
$_SESSION['c'][$num] = $c_letter;
$_SESSION['d'][$num] = $d_letter;
$_SESSION['e'][$num] = $e_letter;
$_SESSION['f'][$num] = $f_letter;

}

$value = function list();

if (!exists)

{
$value

}


else {

$value

}

How does this work please?