> On Apr 15, 2016, at 10:41 AM, Joe Groff <jgr...@apple.com> wrote:
>> On Apr 15, 2016, at 8:29 AM, John McCall via swift-evolution
>> <swift-evolution@swift.org> wrote:
>>
>>> On Apr 14, 2016, at 10:50 PM, Chris Lattner <clatt...@apple.com> wrote:
>>> On Apr 14, 2016, at 10:40 PM, John McCall <rjmcc...@apple.com> wrote:
>>>>>> To me, the unparenthesized style suggests that the input and output are
>>>>>> peers, which feels more natural for the sort of value-to-value
>>>>>> transform/predicate where this most commonly occurs. Parenthesizing the
>>>>>> input feels fussier, which contributes to a sense that the argument is
>>>>>> just one component to producing the result.
>>>>>> The parentheses are grammatically unnecessary in most cases (by
>>>>>> frequency of use in higher-use programming, not by feature count).
>>>>>
>>>>> I agree with your point that many simple higher order programming
>>>>> examples (e.g. map, filter, etc) take a single argument. That said, I
>>>>> don’t agree that this means that we should syntactically privilege this
>>>>> special case.
>>>>
>>>> "Special case" is a loaded phrase. Why is it a special case as a
>>>> parameter if it isn't a special case as a result?
>>>
>>> Because, as I tried to explain in my original post, parameters *are* a
>>> special case. The result type of a function is just a type. The parameter
>>> list allows things that types do not: default arguments and variadics.
>>
>> Default arguments are not allowed in the type grammar. Nor are different
>> internal vs. external labels.
>>
>>> As a concrete example, surely you aren’t arguing that we should support:
>>>
>>> let x : Int… -> Int
>>>
>>> are you?
>>
>> No, but that's because the ... is a reference to the rest of the tuple and
>> doesn't read correctly outside of one.
>>
>>>>>> I guess the flip side is that call and declaration syntax both require
>>>>>> parentheses (unless the only argument is a trailing closure), but again,
>>>>>> we had strong justifications for that: declarations would always be
>>>>>> ambiguous without parens, and calls would have serious problems (and the
>>>>>> style-wars factor would be much larger, especially now with mandatory
>>>>>> keyword arguments by default).
>>>>>
>>>>> Right, but regardless of *why* we always require parens on Decls and
>>>>> ApplyExprs, we really do (and that isn’t going to change). Being
>>>>> consistent between func decls and function types is quite important IMO.
>>>>
>>>> So we should require function argument labels in function types?
>>>
>>> Uhm, yes, we already do. In:
>>>
>>> let x : (a : Int) -> Float
>>> let y : (Int) -> Float
>>> let z : Int -> Float
>>>
>>> x and y have different (but compatible) types. y and z have identical types
>>> (sugared differently).
>>
>> When I said "function type", I was referring to this production in the type
>> grammar, not the type signature component of function declarations. I'm not
>> sure how I could've been clearer on that without actually using the names of
>> grammatical productions.
>>
>> My point was that allowing a function type to be written as "(Int) -> Float"
>> is already inconsistent with function declarations, because that is not
>> legal function declaration syntax; you would have to write "(_ : Int) ->
>> Float".
>>
>> The current language composes naturally here, and your proposal feels like
>> an odd extra rule.
>
> I feel like the current language no longer represents our reality, though (or
> at least, our current ideal vision for reality). We've pretty thoroughly
> broken the "functions have one argument" model.
I don't see this syntax as an offshoot of the "functions always have one
argument" model. I agree that that model is dead.
However, I don't think users require its death to be underlined and written in
bold; it only ever surfaced to them in bugs anyway. But many functions do,
nonetheless, have only one argument; and because of another change to the
model, where argument labels are becoming part of the function's name and not
its type, that argument can be written as just a type.
So to me, this question is whether we add a weird special-case rule that
mandates the use of parentheses because they're required in a bunch of more
complex but less common situations.
> Changing the type grammar to reflect this seems good to me. I would think of
> it as changing the function type grammar to:
>
> function-type ::= '(' (type (',' type)*)? ')' '->' type
>
> which, since the argument list can containing 0, 1, or many individual
> arguments, makes the parens more grammatically necessary.
This is tautological.
John.
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