Re: Passing Global Variables Urgh.

On Aug 29, 4:28 pm, landspeedrecord <landspeedrec...@xxxxxxxxx> wrote:
My only guess is that the function "test2" gets passed a copy of the
global variable that is exists inside the function "test2".

Bingo. Lisp, like most modern languages, is call-by-value. The
`setq' within `test2' only modifies the value of `x'.

But isn't
the whole point of Defvar & Defparameter to create a global variable
that can be accessed from anywhere? If a copy of a global variable is
always passed into functions what good is a global variable?

Now I could write "test2" so that it was:
(defun test2 ()
(setq *x* "orrgoaarghhh"))
but that isn't the same as passing the global variable.

I just don't get it. Urgh???

Lisp never passes variables by reference. You must be coming from
some language (Fortran???) where call-by-reference is the default.

What you can do in Lisp (and Java, and ...) is to bind a global
variable to an object which can then be modified:

(defstruct x-holder
thing)

(defvar *x* (make-x-holder :thing "blargh"))

(defun test2 (x)
(setf (x-holder-thing x) "orrgoaarghhh"))

-- Scott

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