[Zpt] Built-ins and Shadows

[Tim Peters]

[Todd Coram]
>> evan (Mar 2, 2001 10:54 am; Comment #7)
>> (todd's comment #6):
>>>  I strongly feel that the built in names shouldn't be shadowable.
>> We seem to be outnumbered on this one, although Jim agreed that we
>> should generate lots of obnoxious warnings about shadowing of builtins.

[Todd]
> The problem with obnoxious warnings is: when do you generate them
> and where?

When, ASAP; where, I don't know (but somebody else should <wink>).

> Anyway, if shadowing isn't an error (and at the very least we say it is
> something worth issuing warnings about), we should say that the resulting
> behavior is "undefined"  (in terms of the TALES specification) or
> "implementator defined".

That's a dodge taken by language committees when it's impossible to reach
consensus because a dozen vendors already implemented a thing in a dozen
conflicting ways.  It's a last resort, not something to settle for at the
outset!  Shadowing is extremely common-- and well-defined --behavior across
all sorts of language.  Warnings are cool.  The problem with errors is that
if a new builtin name is ever added, then existing code that happens to have
already used that name suddenly becomes illegal "for no reason at all" -- and
users hate that.  The usual shadowing rules ensure that their code continues
to work, albeit with new warnings; much friendlier.