Re: Bug: long strings with REALLY long delimiters …

[Gabriel Bertilson <arboreous.philologist@...>]

[====[[====[]====] works; perhaps you meant ]====]? But actually
]====] can be represented too.

The requirement for representing a string as a long string literal is
that you choose a pair of delimiters such that the closing delimiter
only occurs at the end of the combination of string and closing
delimiter. So if 4 is the maximum number of equals signs in a
delimiter, then if the string is ]====], you can use delimiters with 1
to 3 equals signs: [=[]====]]=], [==[]====]]==], [===[]====]]===]. And
you have to represent the string ] with 1 to 4 equals signs, because
with zero equals signs, [[]]], the closing delimiter appears too
early, and a stray ] is left for the parser to choke on.

So a string that cannot be represented as a long string literal, given
that N is the limit, is one containing every closing delimiter with 0
to N equals signs. If the limit is 4, an unrepresentable string would
be ]]]=]]==]]===]]====]. The minimum length of such a string would be
triangular_number(N) + 2*(N+1). If the limit is 1000, the
unrepresentable string would be at least 502502 bytes long if I
calculated it right. (See the formula below.) It would be very unusual
for such a string to occur in a program.

function unrepr_str_size(limit) local triangle = 0 for i = 1, limit do
triangle = triangle + i end return triangle + 2 * (limit + 1) end

— Gabriel

On Thu, Dec 13, 2018 at 4:11 PM Rena <hyperhacker@gmail.com> wrote:
>
> On Thu, Dec 13, 2018, 16:32 David Favro <lua@meta-dynamic.com wrote:
>>
>>
>>
>> On December 13, 2018 9:01:52 PM UTC, Egor Skriptunoff <egor.skriptunoff@gmail.com> wrote:
>> >On Thu, Dec 13, 2018 at 7:15 PM Roberto Ierusalimschy wrote:
>> >> it seems easier to just
>> >> limit the maximum number of '=' in a long bracket. I don't think
>> >people
>> >> will mind a limit of 1000.
>> >
>> >IMO, it's not a good idea.
>> >If this limit is N, then minimal size of non-quotable string is about
>> >0.5*N^2
>>
>> What's a "non-quotable string"?
>>
>> Am I missing something or can't any string be represented as a literal with e.g. double-quote (") as delimiter and appropriate escaping of special characters?  If so, I don't see your definition of "non-quotable", could you elaborate?
>
>
> A string that starts with `[====[`, assuming the limit of `=` in a delimiter were 4.
>