variable function argument amount

[eluser]plainas[/eluser]
I would like to have a function that would accept sometimes one argument sometimes two.
But whenever i call it with only one argument it throws a php error.

Basically I want both of this to be possible:

mysite.com/index.php/controller/function/arg

mysite.com/index.php/controller/function/arg/another_arg

EDIT: ok, that problem is easily solvable by assigning a default value to optional parameters.
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