Defining a function is only the first step. Generally, one defines a function so that it can be called. With perl, you have to use an extra symbol to specify that you're calling a function, where Python infers it if you put a parameter list. Common Lisp lets you do it either way.

Here's a hypothetical Python:

    mana=foo(100)
    mana(-10)
    mana(-15)

Here's Perl:

    $mana=foo(100);
    &$mana(-10);
    &$mana(-15);

Common Lisp:

    (setf mana (foo 100))
    (funcall mana -10)
    (funcall mana -15)

Also Common Lisp:

    (setf (symbol-function 'mana) (foo 100))
    (mana -10)
    (mana -15)