[swift-evolution] [pitch] Eliminate the "T1 -> T2" syntax, require "(T1) -> T2"
clattner at apple.com
Fri Apr 15 00:50:31 CDT 2016
On Apr 14, 2016, at 10:40 PM, John McCall <rjmccall at 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.
As a concrete example, surely you aren’t arguing that we should support:
let x : Int… -> Int
>>> 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).
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