Is there a way to test a variable for "isForEachable"

Using PHP, is there a function/method/way to check if a variable contains something that would be safe to put into a foreach construct? Something like

//the simple case, would probably never use it this bluntly
function foo($things)
{
    if(isForEachable($things))
    {
        foreach($things as $thing)
        {
            $thing->doSomething();
        }
    }
    else
    {
        throw new Exception("Can't foreach over variable");
    }
}

If your answer is "setup a handler to catch the PHP error", your efforts are appreciated, but I'm looking for something else.