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

[David Sweeris via swift-evolution]

On Oct 2, 2017, at 09:14, Xiaodi Wu <xiaodi...@gmail.com 
<mailto:xiaodi...@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@swift.org <mailto:swift-evolution@swift.org>> wrote:
> 
> On Oct 1, 2017, at 22:01, Chris Lattner via swift-evolution 
> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
> 
>> 
>>> On Oct 1, 2017, at 9:26 PM, Kenny Leung via swift-evolution 
>>> <swift-evolution@swift.org <mailto:swift-evolution@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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