What is a punctuation character?

Iavor Diatchki iavor.diatchki at gmail.com
Sat Mar 17 02:23:48 CET 2012

I am also not an expert but I got curious and did a bit of Wikipedia
reading.  Based on what I understood, here are two (related) questions
that it might be nice to clarify in a future version of the report:

1. What is the alphabet used by the grammar in the Haskell report?  My
understanding is that the intention is that the alphabet is unicode
codepoints (sometimes referred to as unicode characters).  There is no
way to refer to specific code-points by escaping as in Java (the link
that Gaby shared), you just have to write the code-points directly
(and there are plenty of encodings for doing that, e.g. UTF-8 etc.)

2. Do we respect "unicode equivalence"
(http://en.wikipedia.org/wiki/Canonical_equivalence) in Haskell source
code.  The issue here is that, apparently, some sequences of unicode
code points/characters are supposed to be morally the same.  For
example, it would appear that there are two different ways to write
the Spanish letter ñ: it has its own number, but it can also be made
by writing "n" followed by a modifier to put the wavy sign on top.

I would guess that implementing "unicode equivalence"  would not be
too hard---supposedly the unicode standard specifies a "text
normalization procedure".  However, this would complicate the report
specification, because now the alphabet becomes not just unicode
code-points, but equivalence classes of code points.



On Fri, Mar 16, 2012 at 4:49 PM, Ian Lynagh <igloo at earth.li> wrote:
> Hi Gaby,
> On Fri, Mar 16, 2012 at 06:29:24PM -0500, Gabriel Dos Reis wrote:
>> OK, thanks!  I guess a take away from this discussion is that what
>> is a punctuation is far less well defined than it appears...
> I'm not really sure what you're asking. Haskell's uniSymbol includes all
> Unicode characters (should that be codepoints? I'm not a Unicode expert)
> in the punctuation category; I'm not sure what the best reference is,
> but e.g. table 12 in
>    http://www.unicode.org/reports/tr44/tr44-8.html#Property_Values
> lists a number of Px categories, and a meta-category P "Punctuation".
> Thanks
> Ian
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