[swift-evolution] Move placement of 'throws' statement

[Goffredo Marocchi]

I sense s disturbance in the force as if hundreds of pure functional programmers cried in anger ;).

Sent from my iPhone

> On 28 Dec 2016, at 17:52, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> on Tue Dec 27 2016, Chris Lattner <clattner-AT-apple.com> wrote:
>> 
>> On Dec 26, 2016, at 2:55 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> // Move `throws` to the end
>>>> func baz() -> String throws
>>> 
>>> I agree that reads much better.
>> 
>> This doesn’t work unless you’re willing to break consistency with
>> function type syntax, or if you’re willing to make function
>> [type/decl] syntax ambiguous.
>> 
>> How would you express this, for example?
>> 
>>    let x : (_ a : Int) throws -> (_ b: Float) throws -> Double
>> 
>> it would be ambiguous to move the ‘throws’ keyword to the end of the
>> function type, because you'd get:
>> 
>>    let x : (_ a : Int) -> (_ b: Float) -> Double throws throws
> 
> I see.  
> 
> We *could* say that the "throws" keyword comes after the return type
> unless it's a function type, in which case it comes after the return
> type's parameter list
> 
>       let x : (_ a : Int) -> (_ b: Float) throws -> Double throws
> 
> I admit this is a horrible rule from a language designer's point of view
> but there's a chance it could end up being better for users.
> Functions-that-return-functions are, after all, the 0.1% case.
> 
> -- 
> -Dave
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