From: CE Whitehead (firstname.lastname@example.org)
Date: Sun Jul 25 2010 - 15:24:01 CDT
Damn this indecision; I don't know; shall I take an axe to it, or shall I let it grow. --from Judith Wright, "That Seed"
> Date: Sun, 25 Jul 2010 10:43:11 -0600
> From: email@example.com
> To: firstname.lastname@example.org
> CC: email@example.com; firstname.lastname@example.org
> Subject: Re: Reasonable to propose stability policy on numeric type = decimal
> Philippe Verdy wrote:
> > "Kent Karlsson" <email@example.com> wrote:
> >> Den 2010-07-25 03.09, skrev "Michael Everson" <firstname.lastname@example.org>:
> >>> On 25 Jul 2010, at 02:02, Bill Poser wrote:
> >>>> As I said, it isn't a huge issue, but scattering the digits makes the
> >>>> programming a bit more complex and error-prone and the programs a little less
> >>>> efficient.
> >>> But it would still *work*. So my hyperbole was not outrageous. And nobody has
> >>> actually scattered them. THough there are various types of "runs" in existing
> >>> encoded digits and numbers.
> >> While not formally of general category Nd (they are "No"), the superscript
> >> digits are a bit scattered:
> >> 00B2;SUPERSCRIPT TWO
> >> 00B3;SUPERSCRIPT THREE
> >> 00B9;SUPERSCRIPT ONE
> >> 2070;SUPERSCRIPT ZERO
> >> 2074;SUPERSCRIPT FOUR
> >> ...
> >> 2079;SUPERSCRIPT NINE
> >> And there are situations where one wants to interpret them as in a
> >> decimal-position system.
> > Scattering does not only affect decimal digits, but also mathematical
> > operators needed to represent:
> > - the numeric sign (« - » or « + »), with at least two variants for
> > the same system to represent the minus sign (either the ambiguous
> > minus-heighten, the only one supported in many text-to-number
> > conversions, or the true mathematical minus sign U+2212 « − » that has
> > the same width as the plus sign), including some « alternating signs »
> > that exist in two opposite versions (« ± », « ∓ »);
> > - the characters that represent the decimal separator (« . » or « , »)
> > which is almost always needed but locale-specific (this is not just a
> > property of the script);
> > - the optional character used to note exponential notations and used
> > in text-to-number conversion (usually « e » or « E »);
> > - the optional characters used in the conventional formatting for
> > grouping digits (NNBSP alias « fine », with possible automatic
> > fallback to THINSP in font renderers and in rich-text documents
> > controlling the breaking property with separate style, or fallback to
> > NBSP in plain-text documents, or fallback to standard SPACE in
> > preformatted plain-text documents, « , », or « ' », and possibly other
> > punctuations in their « wide » form, for ideographic scripts).
> > Some of them exist in exponential/superscript or indice/subscript
> > versions (notably digits and decimal separators), but not all of them
> > (not all separators for grouping digits, using NNBSP may not be
> > appropriate as its width is not adjusted and it does not have the
> > semantic of a superscript or subscript).
> > For generality, it seems better to assume that digits and other
> > characters needed to note numbers in the positional decimal system may
> > be scattered (libraries may still avoid the small overhead of
> > performing table lookups, by just inspecting a property of the
> > character '0' or of the convention use, that will either say that it
> > starts a contiguous ranges, or that the complete sequence is stored in
> > a lookup array for the 10 digits.
> > The general category "Nd" may not always be accurate to find all
> > digits usable in decimal notations of integers, because the sequence
> > may have been incomplete when it was first encoded, and completed
> > later in scattered positions.
> > In this case, the digits will often have a general property of "No"
> > (or even "Nl") that will remain stable. What should also be stable is
> > their numeric value property (but I'm not sure that this is the case
> > of "Nl" digits, notably for scripts systems using letters in a way
> > similar to Greek or Hebrew letters as digits, even if Greek and Hebrew
> > digits are not encoded separately from the letters that these number
> > notations are borrowing).
> > Also I'm not sure that scripts that define "half-digits", or digits
> > with higher numeric values than 9, are permitting the use of their
> > digits with a numeric value between 0 and 9, in a positional decimal
> > system. The Roman numeric system is such a numeric system (borrowing
> > some scattered Latin letters and adding a few other specific digits)
> > where this will be completely wrong.
> > Or another base than 10 could be assumed by their positional system,
> > even if their digits are encoded in a contiguous range of characters
> > for the subset of values 0 to 9. This is probably no longer the case
> > with scripts that have modern use, but in historical scripts or in
> > historical texts using a modern script, the implied base may be
> > different and would have used more or less distinct digits. So instead
> > of guessing automatically from the encoded text, it may be preferable
> > to annotate the text (easy to insert if the conversion of the
> > historical text uses some rich-text format) to specify how to
> > interpret the numeric value of the original number.
> > And sometimes, the conversion to superscripts/subscripts compatibility
> > characters will not be possible even if some of them may be converted
> > safely to their numeric value, after detecting that they are in
> > superscript/subscript and that they don't behave the same as normal
> > digits (16²⁰ must NOT be interpreted as the numeric value 1620, but
> > must be parsed as two successive numbers 16 and 20, where the second
> > one has the semantic of an exponent, as if there was an exponentiation
> > operator between the two numbers).
> > It is also very frequent that only a few superscript digits will be
> > supported in one font, and other digits may be borrowed from another
> > font using a completely distinct style with distinct metrics or may
> > not be displayed at all (missing glyph). The result is then horrible
> > if you can't predict which font will be used that support the 10
> > digits in a contiguous range of values (even if they are scattered in
> > the code space).
This does seem relevant to me.
> > When converting numbers to text with exponential notations, the use of
> > superscripts should only be used with care, knowing that this won't be
> > possible in all scripts, and that only integers without grouping
> > separators can be used.
> > Some writing systems (unified as « scripts » in Unicode) will still require to:
> > - either use rich-text styling for superscripts used in the
> > conventional notation of exponents,
> > - or use an explicit exponentiation operator, such as the ASCII symbol
> > U+005E "^" (which is not the same as a modifier letter circonflex
> > U+02C6 "ˆ", and that many fonts render at with glyph size and position
> > different from the the combining diacritic and implied by the modifier
> > letter), or a mathemetical operator or modifier letter (like the
> > upward arrow head U+02C4 "˄" that some fonts render as the
> > mathematical wedge operator on the baseline U+2227 "∧", or the less
> > ambiguous upward arrow U+2191 "↑").
> > Philippe.
> That all may be true, but it is really besides the point.
> I'm considering extending an existing computer programming language
> which currently only understands numbers composed solely by the ASCII
> numbers to also understand those from other scripts. I'm not going to
> do it unless it is easy within the existing implementation (not some
> theoretical better implementation) and efficient and not a security threat.
> The symbols for operators like exponentiation are already set in stone.,
> and their being scattered isn't relevant. Likewise, non-decimal-digit
> numbers, like subscripts, are also not relevant.
> I found a way to do the implementation that meets all my criteria, but
> is based on the existing pattern of Gc=Nd (or Nt=De) code point
> assignments. The assignments have so far been prudent, to use Asmus'
> term. I was merely trying to see if this prudence could be codified so
> that my implementation wouldn't get obsoleted on a whim in some future
> Unicode release.
> I hadn't thought of the case where a zero is later found or its usage
> develops in a script, and suddenly all the digits in that script change
> from Nt=Di to Nt=De, which because of an existing stability policy would
> necessarily require their general category changing to Nd.
> Prudence would dictate, then, that when assigning code points to the
> numbers in a script, that a contiguous block of 12-13 be reserved for
> them, such that the first one in the block be set aside for ZERO; the
> next for ONE, etc.
> My original question comes down to then, would it be reasonable to
> codify this prudence? People have said it will never happen. But no
> one has said why that is.
> Obviously, things can happen that will mess this up--the Phaistos disk
> could turn out to be a base-46 numbering system, as an extremely
> unlikely example. But by dictating prudence now, most such eventualities
> wouldn't happen.
> I have since looked at the Nt=Di characters. The ones that aren't in
> contiguous runs are the superscripts and ones that would never be
> considered to be decimal digits, such as a circled ZERO.
Are you proposing that superscripts be in contiguous runs or not? Above you disallowed subscripts (although
I think mathematically subscripts have some meaning in equations as do superscripts and it might worth converting them albeit separately from other numbers; if these were converted it would allow complete equations to be converted from character strings -- but with only digits 1-9 I do not see that much of an issue; I'd personally like to find a subscript i; but so far I've just looked at: http://unicode.org/charts/PDF/U2070.pdf where the subscripts 0-9 are all contiguous but the superscript 1, 2, and 3 are not; searching through http://unicode.org/Public/UNIDATA/UnicodeData.txt that was all I found; I then started going through code charts one by one and so far have gotten as far as Old South Arabian and have not found superscript i or more superscript decimal numbers though maybe I've missed something -- the Arabic sukun is not going to be part of a series of superscripts in any case).
> The only run
> in the BMP which doesn't have a zero is Ethiopic. It seems extremely
> unlikely to me that a zero will be discovered or come into use with that
> script. I'm guessing that they have adopted European numbers in order
> to have commerce with the rest of the world.
> There are several runs in the SMP, but the code point where a zero would
> go isn't assigned.
> I don't know for sure, but it appears to me that we are running out of
> non-dead scripts to encode. I see that draft 6.0 has only 544 BMP code
> points not in any block and not much in the pipeline. I would think
> that most any script yet to be encoded would have borrowed numbering
> systems from their neighbors.
> And there is still plenty of space in the SMP, so this proposal to
> require prudence should not use up too many precious unassigned code points.
If it does not take up too much space; I support this proposal although there is no way that characters are contiguous in any case -- so for doing sorts and such this is not going to help really normally.
C. E. Whitehead
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