How to kill the content of a list instead of the list itself?

On 12/29/2010 6:20 AM, Stefano Ferri wrote:
>
>     I think you have to take into account, that the symbols evaluate to
>     their numerical value.
>
>
> Thank you, maybe I've made a bit of confusion about this point... But 
> there is still an issue: if a, b and c are contained in an unnamed 
> list [a, b, c] they can be killed by apply(kill,'[a,b,c]), and this is 
> clear. The problem comes when the list [a,b,c] is assigned to a variable:
>
> mylist : [a,b,c]
>
> The only solution I've found is this: mylist must either be defined 
> before assigning a value to a, b and c, or defined as
>
> mylist : '[a, b, c]
>
> then apply(kill, mylist) works fine.
First of all, if you do this:  a:1, b:2, c:3

then mylist:[a,b,c]    does not have any of the symbols a,b,c in it.  
All it has is [1,2,3].

Kill is one of the few commands that evaluates its arguments in a 
different fashion:  it doesn't evaluate them.
That means that kill(a)    does not evaluate a to 1, and try to kill 1.  
It just uses the name.
My suggestion is that if you anticipate re-using certain names, you 
insert in your program the command

kill(a,b,c);   before any use of a,b,c.

in fact, it is a good idea, if you repeatedly are loading and testing a 
"batch" file
that the first line be something like

kill(program1, program2, variable1, variable2, ....)    /* clear old 
version of everything out of memory */