On Sat, 2009-11-07 at 05:15 +0100, Pascal J. Bourguignon wrote:
> vj <harik...@gmail.com> writes:
> > I have been programming in LISP for couple of months now.

> To really answer to your following question, we would have to know
> what decendent of LISP do you really use?

> Is that Common Lisp, ISOLisp, LeLisp, Scheme, MacLisp, emacs lisp,
> ZetaLisp, InterLisp, etc, etc, etc?

> > Today, came across a new notation and had a question on that.
> > Let me give an example:

> > I have an access to an "object" [i don't know what the technical term
> > is for a variable of this data-type].

> > (setq some_var data.some_val)

> > by doing the above, i can read the value into some_var.

> Assuming it's Common Lisp, and no special reader trick is active,
> data.some_val is a mere symbol and therefore it is either a normal
> variable as well as some_var, or it is a symbol macro, and probably
> represents some place that is both readable and writeable like a
> normal variable.

> In either case, you can get its value by evaluating directly
> data.some_val, you don't need to store it in some_var.

> Actually, since you've not shown us that you defined the variable
> some_var, some strange things may occur in a Common Lisp
> implementation when you evaluate this setq out of white at the
> toplevel...

> > but the following piece of code is not working and i am not sure if i
> > am even on the right track.

> > (setq read_var data.some_val) # read the value
> > (print read_var) # say the value was originally set to 5, we would see
> > 5 here
> > (setq some_var 18) # sets the value to 18
> > (setq data.some_val some_var) # i expect data.some_val to be set to 18
> > now
> > (setq read_var data.some_val) # read the value just set
> > (print read_var) # i would expect 18 to be displayed. but i still see
> > 5.

> > why would this be?

> It could occur that data.some_val is a symbol macro that expands to an
> accessor, and that the writer method for this accessor doesn't write
> the value for some reason (perhaps the new value is invalid for this
> object?).

> In any case you are not giving us the context, we don't even know what
> language you're speaking of!  So how can we give you a meaningful answer?