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Re: [perl #113554] my() with empty list causes weird error

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Ricardo Signes
June 25, 2012 17:38
Re: [perl #113554] my() with empty list causes weird error
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* Reini Urban <> [2012-06-25T19:43:09]
> Do you really want Perl to compile invalid syntax starting with 5.17
> just because your code generator sucks?

It's not invalid syntax forever just because it was once.

It seems open to change.  The question is: what's the cost, and what's the

The cost at the language level seems minimal.  It does not allow something
semantically absurd, just pointless.  Pointless is okay, if it makes things
simpler under the hood:  perl -e '();;;()=((),,,,())=();;;()'

The benefit at the language level is very small.  It means that when we say
"list," we more often consistently mean "empty is okay, too."  It's still not
great, because we need the parens for the empty list but not a one-element
list.  But that's close to some other uses.  So it brings things just a little
closer to consistency.

So, at the language level, I don't think these changes are too compelling
either way.  I wouldn't see much reason to pick either keeping or changing
things, based on that.  (If nothing else, the error message can definitely be

What about the implementation?  Does it make the life of the implementation
easier to allow C<my ();> ?

> >> >> Why should "my ();" parse correctly?
> >> >> Why should "my;" parse correctly? Both are clearly syntax errors.
> >
> > "my ()" should parse correctly because you'd have to introduce a
> > special case to disallow it. (I'm talking about Perl here, not perl. I
> > don't care much about how it's implemented.)
> I did not disallow it, I changed the error message. It was someone else
> who brought the parser up to MAD inconsistency instead of changing
> the error message and fixing MAD.

He isn't saying that *you* disallowed it.  He means that in the simplest form
of expressing my's definition, "my ();" would accept an empty list, and more
work would be needed for one to expressly disallow it.  To avoid unnecessarily
adding more rules, he says it should be allowed.  (Occam's Razor)


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