Values list (etc.) modified destructively

We have the bug report ID: 712468 "Values list (etc.) modified
destructively".

One simple method might be to support a function which passes a copy of
the global list to the user. E.g.

(defun $values() (copy-list $values))

With such a function we will get

(%i1) a:10;b:20;c:20;
(%o1) 10
(%o2) 20
(%o3) 20

(%i4) x:values();  /* Store a copy in x */
(%o4) [a,b,c]

(%i5) values;      /* This is not a copy */
(%o5) [a,b,c,x]

(%i6) values();    /* Output of a copy */
(%o6) [a,b,c,x]

(%i7) kill(a);     /* We kill the first entry */
(%o7) done

(%i8) x;           /* The value of x is not destroyed */
(%o8) [a,b,c]

(%i9) %o6;         /* %o6 is a copy of the list */
(%o9) [a,b,c,x]

(%i10) %o5;        /* But not %o5, the first entry is missing */
(%o10) [b,c,x]

But we can do it the following way too:

(%i13) y:copy(values);
(%o13) [b,c,x]

(%i14) kill(b);
(%o14) done

We have killed b, but the values of y and %o13 are not modified,

(%i15) y;
(%o15) [b,c,x]

(%i16) %o13;
(%o16) [b,c,x]

So, if we have a bug we might support a function to pass a copy of the
list to the user. Furthermore, it might be desirable to hide the
internal global list from access by the user.

If the current behavior is not a bug, it might be sufficient to document
it and give a hint to use the function copy if a real copy is necessary.

Dieter Kaiser