How to properly handle a function that needs a variable?

[eluser]Chris.Campbell[/eluser]
If I have a function that expects a variable from the URL, how to I properly redirect if the user modifies the URL so the variable does not exist? I cannot figure out how to use the redirect function.

[eluser]BrandonDurham[/eluser]

Code:

function functionName($var=NULL)
{
    if (!$var) ...
}

[eluser]Chris.Campbell[/eluser]
Solved. Make sure you load the URL helper