Re: U+FFFF

"Richard A. O'Keefe" <[email protected]> Tue, 30 Jul 2013 09:46:26 +1200

Newsgroups	gmane.comp.ai.prolog.swi
Message-ID	<[email protected]>

On 30/07/2013, at 12:58 AM, 申远 wrote:

> I have a U+FFFF in my .pl file,which is coded in UTF-8.

It is definitely ungood for a program to silently accept
non-character codes (we had a long thread about that, in
I think the standard mailing list).  But it is far worse
for a program to generate such a thing to begin with.

So how did that U+FFFF get there?

> There is no error when I consulted it in swi-prolog,
> where there is a error when I consulted it in tu-prolog.

Getting full Unicode-correctness is appallingly hard.
The Unicode 6.1 book is about 660 pages long -- bigger
than the phone book in this city! -- and that does NOT
include any character tables any more.  It is full to
overflowing with quirky little details.

The Java compiler (javac 1.7.0_13, just tested) will
let you use '\uFFFF' and "\uFFFF" freely, even at the
highest "lint" setting.

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