I’m all for fixing pressing issues requested by Xiaodi, but beyond that I
request we give a little more thought to the long term direction.
My 2¢ is I’ve been convinced that very few characters are “obviously” either a
operator or identifier across all contexts where they might be used. Thus
relegating the vast majority of thousands of ambiguous characters to committee
to decide a single global usage. But that is both a huge time sink and
fundamentally flawed in approach due to the contextual dependency of who is
using them.
For example, if a developer finds a set of symbols which perfectly denote some
niche concept, do you really expect the developer to submit a proposal and wait
months/years to get the characters classified and then a new compiler version
to be distributed, all so that developer can adopt his/her own notation?
And then after that is done, now say a member of some distant tribe complains
they wanted to use one of those characters to write identifiers using their
native language. Even though there may be zero intersection between these two
user groups, this path forces Swift itself to pick a side of one vs. the other.
Surely there is some way to enable the local developer to resolve these choices
rather than putting the swift language definition on the critical path?
The goals I know of:
1. Performance: don’t require parsing all imports to get the operator set
2. Security: don’t let imports do surprising/obfuscated stuff
3. Functionality: do let users write what they want, or import/share libraries
for niche domains
4. Well defined: resolve conflicts, e.g. between libraries
I’m a little out of my league, but let’s say we want to use operator ᵀ from
some matrixlib, how about:
import matrixlib (operator: ᵀ)
Or if you want several operators:
import matrixlib (operators: [ᵀ,·,⊗])
Ideally, any local operator definitions “just work” across their own module,
but if it requires a “import (operator: ×)” in each file for performance, so be
it.
A whitelist of “standard” operators would automatically import (i.e. initialize
the operator character list) to maintain compatibility with current usage. But
you can imagine additional arguments to the import call, such as
“standardOperators: false” to import only the explicitly listed operators and
reduce potential surprises.
My rationale vs. the goals:
1. Performance: the operator character set vs. identifiers (everything else)
can be determined within the file itself
2. Security: developer explicitly opts-in to the special operators they want to
use, and readers can see where an operator comes from
3. Functionality: user is able to define their operators without getting
committee involved
4. Well defined: potential conflict between libraries resolved by client’s
choice to import or exclude the operator
Does this have potential?
-Ethan
> On Oct 2, 2017, at 10:59 AM, David Sweeris via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>
> 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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