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- Subject: Re: Lua 5.4: question about label visibility rule
- From: Arnaud Delobelle <arnodel@...>
- Date: Wed, 19 Jan 2022 12:41:35 +0000
On Wed, 19 Jan 2022 at 12:18, Albert Krewinkel <email@example.com> wrote:
> Arnaud Delobelle <firstname.lastname@example.org> writes:
> > In the Lua 5.4 docs it says the following.
> > > A label should not be declared where a label with the same
> > > name is visible, even if this other label has been declared
> > > in an enclosing block.
> > I have found the following test in the Lua 5.4.3 Test Suite (available
> > here: http://www.lua.org/tests/), in the file goto.lua (starting line
> > 223):
> > [...]
> > In this function the label ::l1:: is declared twice, once in the
> > "elseif a == 4" clause and once at the end of the function. In my
> > understanding, the second declaration of this label is visible at the
> > point where the first declaration is made. That would contravene the
> > rule I have quoted above.
> I believe the cited paragraph from the docs must be read as a
> recommendation rather than a rule: the label *should not* be declared,
> but if people do, the behavior is still well-defined (and tested in the
> test suite). RFC 2119 phrases it best:
> > 4. SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that
> > there may exist valid reasons in particular circumstances when the
> > particular behavior is acceptable or even useful, but the full
> > implications should be understood and the case carefully weighed
> > before implementing any behavior described with this label.
It could be an interpretation but I do not think that is the case.
Take for example the following program:
----- testlabel.lua ----
---- end ----
If I run this with Lua 5.4.3 I get the following output:
lua: testlabel.lua:5: label 'foo' already defined on line 2
If I run it with Lua 5.3 it compiles and run (forever!). This shows
that Lua 5.4.3 enforces the rule I quoted (to an extent) so I believe
my question remains.