PHP: Assign multiple variables in if statement

I don't seem to be able to assign multiple variables in an "if" statement. The following code:

<?php

function a ($var)
{
    if ($var == 1)
    {
        return 'foo';
    }

    return false;
}

function b ($var)
{
    if ($var == 1)
    {
        return 'bar';
    }

    return false;
}

if ($result1 = a(1) && $result2 = b(1))
{
    echo $result1 . ' ' . $result2;
}

?>

Returns "1 bar" rather than "foo bar". If I remove the second condition/assignment it returns "foo".

Is there a way to assign multiple variables in an "if" statement or are we limited to just one?