[swift-evolution] A path forward on rationalizing unicode identifiers and operators

[David Sweeris]

On Oct 2, 2017, at 09:14, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:

> What is your use case for this?
> 
> On Mon, Oct 2, 2017 at 10:56 David Sweeris via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
> On Oct 1, 2017, at 22:01, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> 
>>> On Oct 1, 2017, at 9:26 PM, Kenny Leung via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> Hi All.
>>> 
>>> I’d like to help as well. I have fun with operators.
>>> 
>>> There is also the issue of code security with invisible unicode characters and characters that look exactly alike.
>> 
>> Unless there is a compelling reason to add them, I think we should ban invisible characters.  What is the harm of characters that look alike?
> 
> Especially if people want to use the character in question as both an identifier and an operator: We can make the character an identifier and its lookalike an operator (or the other way around).

Off the top of my head...
In calculus, “𝖽” (MATHEMATICAL SANS-SERIF SMALL D) would be a fine substitute for "d" in “𝖽y/𝖽x” ("the derivative of y(x) with respect to x").
In statistics, we could use "𝖢" (MATHEMATICAL SANS-SERIF CAPITAL C), as in "5𝖢3" to mimic the "5C3" notation ("5 choose 3"). And although not strictly an issue of identifiers vs operators, “！” (FULLWIDTH EXCLAMATION MARK) would be an ok substitution (that extra space on the right looks funny) for "!" in “4！” ("4 factorial").

I'm sure there are other examples from math/science/<insert any "symbology"-heavy DSL here>, but “d” in particular is one that I’ve wanted for a while since Swift classifies "∂" (the partial derivative operator) as an operator rather than an identifier, making it impossible to use a consistent syntax between normal derivatives and partial derivatives (normal derivatives are "d(y)/d(x)", whereas partial derivatives get to drop the parens "∂y/∂x")

- Dave Sweeris
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