Turn array into independent function arguments - howto?

I want to use values in an array as independent arguments in a function call. Example:

// Values "a" and "b"
$arr = array("alpha", "beta");
// ... are to be inserted as $a and $b.
my_func($a, $b)
function my_func($a,$b=NULL) { echo "{$a} - {$b}"; }

The number of values in the array are unknown.

Possible solutions:

1. I can pass the array as a single argument - but would prefer to pass as multiple, independent function arguments.

2. implode() the array into a comma-separated string. (Fails because it's just one string.)

3. Using a single parameter:

   $str = "'a','b'";
   function goat($str);  // $str needs to be parsed as two independent values/variables.
   

4. Use eval()?

5. Traverse the array?

Suggestions are appreciated. Thanks.