[swift-evolution] define backslash '\' as a operator-head in the swift grammar

Mon Feb 6 15:28:16 CST 2017

Although there was, as you say, some push-back against revamping our set of
operator characters, there was also substantial push-forward. Many people
want to resolve the problematic situation we currently have regarding the
designation of operators and identifiers.

And indeed, cutting back to ASCII-only operators would have been an
abominable choice. However waiting for the Unicode Consortium to draft
guidelines for operator characters means prolonging our existing
predicament. Additionally, in the discussion last fall it was mentioned
that Unicode personnel are aware of what we are doing with Swift operators,
and that our decisions may help to inform their classification of operator
characters:

On Fri, Oct 21, 2016 at 5:38 PM, Jonathan S. Shapiro <jonathan.s.shapiro@
gmail.com> wrote:

> That's a feasible way to go, but keep in mind that the UAX31 changes are
> being co-designed with and informed by the current discussion. There are a
> bunch of things that have come up here that will allow UAX31 to side-step
> some "might have happened" mistakes, so this discussion has been very
> useful.
>
> The Swift community can and should make its own decision about whether to
> remain engaged. The risk of disengagement is that messy compatibility
> issues will probably have to be faced later that we can easily head-off now.

Given all these considerations, I think the principled approach is for us
to move forward with a 3-part categorization of characters into operators,
identifiers, and unspecified (to be determined). That way we need not
harangue ourselves over every controversial glyph, and may instead quickly
determine those characters which should definitely be operators and those
which should definitely be identifiers, while saving the difficult
decisions until such time as Unicode produces recommendations and/or we
decide to undertake a more comprehensive review.

Nevin

On Sun, Feb 5, 2017 at 8:29 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:

> IIRC, where we left the discussion last time was that there was work not
> yet complete within Unicode on delineating identifier and operator
> characters. As there was broad agreement to align identifier characters
> with Unicode standards, and since the strict separation between identifiers
> and operators means that no character should belong to both, there was
> hesitation to declare an operator what Unicode may later deem to be an
> identifier.
>
> There was strenuous objection to temporarily cutting back operators to the
> ASCII range until Unicode completes its work, but also pushback in going
> character-by-character above the ASCII range.
>
> In any case, \ seems perfectly reasonable as an additional operator
> character that doesn't have to wait for Unicode.
>
> On Sun, Feb 5, 2017 at 19:02 T.J. Usiyan via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> +1 from me.
>>
>> I hope that operators get more work soon, especially with regard to math.
>>
>> On Sun, Feb 5, 2017 at 5:09 PM, Nevin Brackett-Rozinsky via
>> swift-evolution <swift-evolution at swift.org> wrote:
>>
>> +1 as well. I also support adding these four symbols: ⅀ ؆ ؇ ⅋ as
>> operators.
>>
>> There was substantial discussion last fall about revamping operators in
>> Swift, with the primary goal of removing characters that should not be in
>> the set. I went through the Unicode tables and compiled a list of 1,020
>> characters that I think definitely should be operators [list of operator
>> characters
>> <http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%5B%3ASm%3A%5D%0D%0A%0D%0A-%5Cp%7BBlock%3DSuperscripts+And+Subscripts%7D%0D%0A-%5Cp%7BBlock%3DMiscellaneous+Technical%7D%0D%0A-%5Cp%7BBlock%3DGeometric+Shapes%7D%0D%0A-%5Cp%7BBlock%3DMiscellaneous+Symbols%7D%0D%0A-%5Cp%7BBlock%3DAlphabetic+Presentation+Forms%7D%0D%0A-%5Cp%7BBlock%3DSmall+Form+Variants%7D%0D%0A-%5Cp%7BBlock%3DHalfwidth+And+Fullwidth+Forms%7D%0D%0A-%5Cp%7BBlock%3DMathematical+Alphanumeric+Symbols%7D%0D%0A-%5Cp%7BBlock%3DArabic+Mathematical+Alphabetic+Symbols%7D%0D%0A-%5Cp%7Bsubhead%3DVariant+letterforms+and+symbols%7D%0D%0A-%5Cp%7Bsubhead%3DLetterlike+symbol%7D%0D%0A%0D%0A%5Cp%7BBlock%3DArrows%7D%0D%0A%5B%2F+%3D+%5C-+%2B+%21+*+%25+%3C+%3E+%5C%26+%7C+%5C%5E+~+%3F%5D%0D%0A%5B%C2%A1+%C2%A2+%C2%A3+%C2%A4+%C2%A5+%C2%A6+%C2%A7+%C2%A9+%C2%AB+%C2%AC+%C2%AE+%C2%B0+%C2%B1+%C2%B6+%C2%BB+%C2%BF%5D+-+%5B%C2%A2+%C2%A3+%C2%A4+%C2%A5+%C2%A9+%C2%AE%5D%0D%0A%5Cp%7Bsubhead%3DGeneral+punctuation%7D+-+%5BU%2B203F+U%2B2040+U%2B2045+U%2B2046+U%2B2054%5D%0D%0A%5Cp%7Bsubhead%3DDouble+punctuation+for+vertical+text%7D%0D%0A%5Cp%7Bsubhead%3DArchaic+punctuation%7D+-+%5BU%2B2E31+U%2B2E33+U%2B2E34+U%2B2E3F%5D%0D%0AU%2B214B%5D&g=&i=>
>> ]
>>
>> The effect of that would be to make 1,628 characters no longer usable as
>> operators [list of non-operator characters
>> <http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%2F+%3D+%5C-+%2B+%21+*+%25+%3C+%3E+%5C%26+%7C+%5C%5E+~+%3F%0D%0AU%2B00A1+-+U%2B00A7%0D%0AU%2B00A9+U%2B00AB+U%2B00AC+U%2B00AE%0D%0AU%2B00B0+-+U%2B00B1%0D%0AU%2B00B6+U%2B00BB+U%2B00BF+U%2B00D7+U%2B00F7%0D%0AU%2B2016+-+U%2B2017%0D%0AU%2B2020+-+U%2B2027%0D%0AU%2B2030+-+U%2B203E%0D%0AU%2B2041+-+U%2B2053%0D%0AU%2B2055+-+U%2B205E%0D%0AU%2B2190+-+U%2B23FF%0D%0AU%2B2500+-+U%2B2775%0D%0AU%2B2794+-+U%2B2BFF%0D%0AU%2B2E00+-+U%2B2E7F%0D%0AU%2B3001+-+U%2B3003%0D%0AU%2B3008+-+U%2B3030%5D%0D%0A%0D%0A-%5B%5B%3ASm%3A%5D%0D%0A-%5Cp%7BBlock%3DSuperscripts+And+Subscripts%7D%0D%0A-%5Cp%7BBlock%3DMiscellaneous+Technical%7D%0D%0A-%5Cp%7BBlock%3DGeometric+Shapes%7D%0D%0A-%5Cp%7BBlock%3DMiscellaneous+Symbols%7D%0D%0A-%5Cp%7BBlock%3DAlphabetic+Presentation+Forms%7D%0D%0A-%5Cp%7BBlock%3DSmall+Form+Variants%7D%0D%0A-%5Cp%7BBlock%3DHalfwidth+And+Fullwidth+Forms%7D%0D%0A-%5Cp%7BBlock%3DMathematical+Alphanumeric+Symbols%7D%0D%0A-%5Cp%7BBlock%3DArabic+Mathematical+Alphabetic+Symbols%7D%0D%0A-%5Cp%7Bsubhead%3DVariant+letterforms+and+symbols%7D%0D%0A-%5Cp%7Bsubhead%3DLetterlike+symbol%7D%0D%0A%5Cp%7BBlock%3DArrows%7D%0D%0A%5B%2F+%3D+%5C-+%2B+%21+*+%25+%3C+%3E+%5C%26+%7C+%5C%5E+~+%3F%5D%0D%0A%5B%C2%A1+%C2%A2+%C2%A3+%C2%A4+%C2%A5+%C2%A6+%C2%A7+%C2%A9+%C2%AB+%C2%AC+%C2%AE+%C2%B0+%C2%B1+%C2%B6+%C2%BB+%C2%BF%5D+-+%5B%C2%A2+%C2%A3+%C2%A4+%C2%A5+%C2%A9+%C2%AE%5D%0D%0A%5Cp%7Bsubhead%3DGeneral+punctuation%7D+-+%5BU%2B203F+U%2B2040+U%2B2045+U%2B2046+U%2B2054%5D%0D%0A%5Cp%7Bsubhead%3DDouble+punctuation+for+vertical+text%7D%0D%0A%5Cp%7Bsubhead%3DArchaic+punctuation%7D+-+%5BU%2B2E31+U%2B2E33+U%2B2E34+U%2B2E3F%5D%0D%0AU%2B214B%5D&g=&i=>
>> ]
>>
>> However, my strategy was to be conservative in accepting operators. There
>> are several Unicode blocks which contain some additional characters which
>> we may want to have as operators [list of characters in those blocks
>> <http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%5Cp%7BBlock%3DMiscellaneous+Technical%7D%0D%0A%5Cp%7BBlock%3DOptical+Character+Recognition%7D%0D%0A%5Cp%7BBlock%3DBox+Drawing%7D%0D%0A%5Cp%7BBlock%3DBlock+Elements%7D%0D%0A%5Cp%7BBlock%3DGeometric+Shapes%7D%0D%0A%5Cp%7BBlock%3DMiscellaneous+Symbols%7D%0D%0A%5Cp%7BBlock%3DDingbats%7D%0D%0A%5Cp%7BBlock%3DBraille%7D%0D%0A%5Cp%7BBlock%3DMiscellaneous+Symbols+And+Arrows%7D%0D%0A%5Cp%7BBlock%3DYijing+Hexagram+Symbols%7D%0D%0A%5Cp%7BBlock%3DMusical+Symbols%7D%0D%0A%5Cp%7BBlock%3DAncient+Greek+Musical+Notation%7D%0D%0A%5Cp%7BBlock%3DTai+Xuan+Jing+Symbols%7D%0D%0A%5Cp%7BBlock%3DMahjong+Tiles%7D%0D%0A%5Cp%7BBlock%3DDomino+Tiles%7D%0D%0A%5Cp%7BBlock%3DPlaying+Cards%7D%0D%0A%5Cp%7BBlock%3DOrnamental+Dingbats%7D%0D%0A%5Cp%7BBlock%3DAlchemical+Symbols%7D%0D%0A%5Cp%7BBlock%3DGeometric+Shapes+Extended%7D%0D%0A%5Cp%7BBlock%3DSupplemental+Arrows+C%7D%5D%0D%0A&g=&i=>
>> ]
>>
>> I did not include the backslash because I decided not to mess with the
>> choice of ASCII operators, however I do support making backslash an
>> operator. I am not sure about currency symbols.
>>
>> Nevin
>>
>>
>> On Sun, Feb 5, 2017 at 1:20 PM, Dave Abrahams via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>
>> on Sun Feb 05 2017, Nicolas Fezans <swift-evolution at swift.org> wrote:
>>
>> > Dear all,
>> >
>> > This is a rather simple proposal to add '\' (backslash character) as a
>> > valid operator-head in the swift grammar.
>> >
>> > One argument for it, is that there exist a backslash operator in the
>> > MATLAB/Scilab/Octave languages. In this languages A\B solves the linear
>> > system A*X = B for X (or the least square problem associated to it if
>> the
>> > system of equations is overdetermined). I am doing some numerical
>> > computation in Swift and it would be nice to be able to declare the same
>> > operator name for this functionality.
>> >
>> > I might have missed some arguments for not adding them, but I seems to
>> me
>> > that until now the \ character is only used inside of string literals.
>> If
>> > that is the case, both uses should never generate a conflict or be
>> > ambiguous, isn't it? (String literals keep their interpretation of \
>> and \
>> > used otherwise within the swift code will be interpreted as an operator
>> or
>> > as the beginning of an operator)
>> >
>> > I am curious to see what will be the feedback on this.
>>
>> +1 if it doesn't clash with the grammar.
>>
>> --
>> -Dave
>>
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