RE: Reasonable to propose stability policy on numeric type = decimal

From: CE Whitehead (
Date: Sun Jul 25 2010 - 15:24:01 CDT

  • Next message: CE Whitehead: "RE: Reasonable to propose stability policy on numeric type = decimal"

    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:
    > To:
    > CC:;
    > Subject: Re: Reasonable to propose stability policy on numeric type = decimal
    > Philippe Verdy wrote:
    > > "Kent Karlsson" <> wrote:
    > >> Den 2010-07-25 03.09, skrev "Michael Everson" <>:
    > >>> 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:
    > >>
    > >> 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: where the subscripts 0-9 are all contiguous but the superscript 1, 2, and 3 are not; searching through 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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