Re: Ambiguous syntax

[Sven Olsen <sven2718@...>]

There's no honest ambiguity in the syntax -- it's just a question of protecting against likely bugs.

f()

(g or h)()

is naturally read as 2 statements, though given Lua's grammar it should be parsed as just one.  Lua 5.1 was newline sensitive: it would throw an error if an otherwise complete _expression_ was continued by a newline, followed by an open paren.  Lua 5.2 removed the check.

My feeling is that this was a bad change -- I've never come across a case where the error was triggered by bug-free code.  I've actually changed my own 5.2 parser to restore 5.1's newline sensitivity, though, rather than throwing an error, I just terminate the _expression_ -- and I wrote a long post about the pros and cons of this idea, a few months back :)

-Sven

On Tuesday, December 11, 2012, Peter Loveday wrote:

This does it in 5.1:

print
("hello")

- Peter


-----Original Message----- From: Coda Highland
Sent: Wednesday, December 12, 2012 5:10 PM
To: Lua mailing list
Subject: Re: Ambiguous syntax

On Tue, Dec 11, 2012 at 10:00 PM, Dirk Laurie <dirk.laurie@gmail.com> wrote:

Can someone who understands the matter please explain
why Lua 5.1 sometimes gave the message

    ambiguous syntax (function call x new statement)

whereas Lua 5.2 never does?

I think I remember hearing about 5.2 arbitrarily defining a resolution
for the grammatical ambiguity. Do you have an example of code that
triggers this?

/s/ Adam



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