inconsistent push operator behaviour

[gamato]

$ qore -n -e 'list l = (1,2); printf("%n\n", l);'
list: (1, 2)

$ qore -n -e 'list l = (1,2); delete l; printf("%n\n", l);'

$ qore -n -e 'list l = (1,2); delete l; push l, 3; printf("%n\n", l);'
list: (3)

$ qore -n -e 'softlist l = (1,2); delete l; push l, 3; printf("%n\n", l);'

[tethal]

I assume that for the *list list type this is ok:

$ qore -n -e '*list l = (1, 2); delete l; push l, 3; printf("%n\n", l);'
<NOTHING>

since the default for *list is NOTHING and not an empty list.

However, for the unshift operator we get this:

$ qore -n -e '*list l = (1, 2); delete l; unshift l, 3; printf("%n\n", l);'
unhandled QORE System exception thrown in TID 1 at 2015-12-29 10:05:53.408376 Tue +01:00 (CET) at <command-line>:1
UNSHIFT-ERROR: first argument to unshift is not a list

which is a completely different inconsistency.

[tethal]

After discussion the exception produced by unshift seems reasonable so we will implement this for other list operators as well

[davidnich]

in order not to break backward compatibility, the runtime exceptions will only be thrown if %strict-args is in effect