[swift-evolution] [Discussion] Parentheses

[Jens Persson]

I'll try to rephrase my initial post a bit, perhaps it will make my point
clearer:

Might it be that some of the confusion regarding the evolution
(design/redesign) of tuples, parameter lists, etc. stems from the fact that
they all use parentheses? Or put differently: Parentheses, being used for
so many different (and similar) things, is perhaps blurring the "real"
(possibly simpler) similarities and differences.

I'm not saying they should not all use parentheses in the final design, I'm
only saying that perhaps it is making it harder to think clearly about
these things (while designing  the language).

Let's say we carry out a thought-experiment in which we assume that argument
and parameter lists use eg ≪≫ and tuples use eg ⊂⊃, and normal parentheses
are _only_ used for grouping and controlling priority in eg mathematical
expressions, but not when creating tuples, parameter lists, pattern
matching and closure types.

Using this notation (which is just a thinking-tool, not meant as a final
syntax), and reimagining these things from scratch, we could for example
try and see what happens if we assume that these are three _different_
types:
Int
⊂Int ⊃
⊂⊂ Int ⊃⊃
and also, for example, that it is ok to have single element tuples with an
element label.
And:

((-1) * ((x + y) + (3 * y))) // Still OK. Redundant parens are treated as
usual / as before.

⊂ String, Int ⊃ // Two element tuple type whose elements are a String and
an Int.

⊂ Int ⊃ // Single element Tuple type.

⊂⊂ Int ⊃⊃ // Single element Tuple type whose only element is another single
element tuple type whose only element is an Int.

≪ Int ≫ -> Int // Function type from Int to Int.

Perhaps the ≪≫ would prove to be unnecessary, so:

Int -> Int // Function type from Int to Int.
(Int -> Int)? // Optional function type from Int to Int.
((((Int -> Int))))? // Optional function type from Int to Int. (remember
parens are _only_ used for grouping this way)

⊂ Int, Int, Int ⊃ -> Int // Function type from a 3-Int-tuple to an Int.
⊂⊂ Int, Int, Int ⊃⊃ -> Int // Function type from a single element tuple
whose element is a 3-Int-tuple to an Int. (Yes, nobody would probably write
a function of such a type, but allowing it could perhaps make the rules a
lot simpler.)

... Well, I think you get the idea.

I'm wondering if there has been any attempts at such from-the-scratch
redesigns of all these parentheses-related-things in the language
(including eg pattern matching, associated values and more).

/Jens


On Wed, Jul 6, 2016 at 8:10 PM, Vladimir.S via swift-evolution <
swift-evolution at swift.org> wrote:

> On 06.07.2016 20:51, Joe Groff wrote:
>
>>
>> On Jul 6, 2016, at 7:47 AM, Vladimir.S via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>>
>>> On 06.07.2016 3:57, Jens Persson via swift-evolution wrote:
>>>
>>>> Please feel free to ignore this naive attempt to engage in this
>>>> discussion.
>>>>
>>>> My understanding of the history of Swift's tuples, argument lists,
>>>> pattern
>>>> matching, associated values, etc. in two steps:
>>>>
>>>> 1. Initial Idealism *:
>>>> Simple powerful heavily reused general concept.
>>>>
>>>> 2. Iterative pragmatism / reality *:
>>>> Complicated (exceptions to) rules.
>>>>
>>>> (* Inevitably not taking everything in to account.)
>>>>
>>>> Has there been any recent attempts to outline a more or less complete
>>>> redesign for these things, returning to step 1 so to speak, but taking
>>>> into
>>>> account what has now been learned?
>>>>
>>>>
>>>> As a side note (and supposedly trivial to most but me):
>>>>
>>>> Parentheses (parenthesized expressions in the grammar?) are used for
>>>> all of
>>>> these parts of the language, and they probably should be, but perhaps
>>>> the
>>>> similarities and differences between the language constructs can be made
>>>> clearer to see by pretending that argument and parameter lists are
>>>> written
>>>> with eg ≪≫ and tuples with eg ⊂⊃, etc.?
>>>>
>>>> For example, I think most people agree that we should be able to use
>>>> "sloppy/forgiving" parenthetical grouping in code such as:
>>>> ((1 + (2 * 3)) * (x + (-5))) - y
>>>> This is fine and can be used to express meaning for the person
>>>> reading/writing, even though it means that some of the parens can become
>>>> superfluous to a machine interpretation.
>>>>
>>>> AFAICS this need not have anything to do with tuples and/or parameter
>>>> lists, but the fact that Swift is treating eg:
>>>> func foo(x: ((((Int))))) { print(x) }
>>>> as
>>>> func foo(x: Int) { print(x) }
>>>> and
>>>> ((Int, Int))
>>>> as
>>>> (Int, Int)
>>>>
>>>
>>> If SE-0110 will be accepted, ((Int, Int)) will mean "1 tuple with
>>> Int,Int fields" and (Int, Int) will mean only "list of two Ints in
>>> parameters"
>>>
>>
>> ((Int, Int)) would still be equivalent to (Int, Int). SE-0110 only
>> concerns parameter lists in function types.
>>
>
> Yes, I'm talking about parameter list in function. Perhaps I'm missing
> something... Quotation from proposal:
>
> >----------------<
> To declare a function type with one tuple parameter containing n elements
> (where n > 1), the function type's argument list must be enclosed by double
> parentheses:
>
> let a : ((Int, Int, Int)) -> Int = { x in return x.0 + x.1 + x.2 }
> >----------------<
>
> Oh... Or do you(and Jens) mean that this:
> let x : (Int, Int) = (1,2)
> will be the same as this:
> let x : ((Int, Int)) = (1,2)
> ? and about
> func foo(_ x: ((Int, Int))) { print(x) }
> vs
> func foo(_ x: (Int, Int)) { print(x) }
> ?
> In this case yes, sorry for misunderstanding, SE-0110 will not change
> this. I don't see any ambiguity here: foo will be called as
> foo((1,2)) - clearly that tuple is sent as argument.
>
>
>
>> -Joe
>>
>>
>>> seems to suggest that it somehow does.
>>>>
>>>> Or maybe I have just forgotten the reasons for why there can be no such
>>>> thing as (a nested) single element tuple (type).
>>>>
>>>> I also can't remember what the pros & cons of disallowing labeled single
>>>> element tuples were.
>>>>
>>>> Happy to be corrected and pointed to relevant reading : )
>>>>
>>>> /Jens
>>>>
>>>>
>>>>
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>>>>
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>>
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