[REBOL] Re: On mutability and sameness
From: lmecir:mbox:vol:cz at: 17-Jun-2001 10:02
> > a sample thought (you need not take it seriously):
> But I *always* take you seriously! ;-)
> > > MY MODEL:
> > >
> > > a) All set-path expressions cause something to be mutated.
> > > The "something" is identified by the set-path up to the
> > > last #"/" and which part of that "something" is identified
> > > by what follows the last #"/". Any such "something" is
> > > mutable.
> > A possible POV: once upon a time the time values in Rebol
> > behaved like:
> > a: 12:30 ; == 12:30
> > a/hour: 13 ; == 13:30
> > a ; == 12:30
> I don't know if anyone else did, but I reported that behavior
> to RT as questionable. In a subsequent release, it was changed.
> I conclude that either someone changed his mind, or that the
> original behavior was a bug.
> > Back then your rule was incorrect. Your rule hasn't changed
> > since then and therefore it is still incorrect.
> Actually, the prior behavior led me to conclude that TIME!
> values were immutable, and I stated so at the time (pardon the
> pun ;-). Now that that behavior has changed, I conclude that
> TIME! values are mutable.
> I did not state the simplified "rule" above until *after*
> TIME! values became mutable.
I try to reformulate my argument: "your rule is correct only in the
circumstances not specified by the rule"
This is a sufficient condition for the rule to be considered incorrect.