[Haskell-cafe] Valid Haskell characters

[Richard A. O'Keefe]

On 26 Aug 2008, at 3:42 pm, Deborah Goldsmith wrote:

> All characters with general category Lu have the property Uppercase,  
> but the converse is not true.

It depends on what the OP wants to do with the information.
For example, Unicode Standard Annex 31,
http://www.unicode.org/reports/tr31/tr31-9.html
is defined in terms of the General Character classification,
*not* in terms of the binary properties "Upper", "Alpha", &c.

When the Haskell report says
	uniSmall -> any Unicode lowercase letter
	uniLarge -> any uppercase or titlecase Unicode letter
it is really unclear what definition is meant: are we talking
about characters in general category Lu or Lt, or are we
talking about characters with the Uppercase property?
Since it's _identifiers_, I'd expect UAX#31 to apply, so it
should be general category.

The specification of the Char module is similarly ambiguous.
Since this is *not* about identifiers, I suppose this time
the Other_Uppercase characters might well be included.

It would be nice to have this spelled out clearly somewhere
not too far from the Report on haskell.org.