> On Dec 13, 2017, at 10:20 AM, Stephen Celis via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>> On Dec 11, 2017, at 1:08 PM, Matthew Johnson via swift-evolution
>> <swift-evolution@swift.org> wrote:
>>
>> It’s worth mentioning that the problem this thread is discussing can be
>> generalized to idioms / applicative. The specific case here is for Optional
>> but many other types could benefit from an elegant syntactic solution to
>> this problem. It might be worth exploring a more general solution. Here’s
>> a link to how this is handled in Idris:
>> http://docs.idris-lang.org/en/latest/tutorial/interfaces.html#idiom-brackets.
>>
>> Matthew
>
> Just want to +1 a more general, less "Optional"-specific solution. You can do
> a ton of interesting things with applicative structure.
>
Chris L had a beautiful solution for an "Unwrappable" protocol that allowed all
of the optional sugar to be extended to any type that had a biased `Wrapped`
item, allowing it to be used with `Either`, `Wrapped`, etc as well as form the
basis for `Optional` itself.
protocol Unwrappable {
associatedtype Element
func unwrap() -> Element?
}
I have a proposal around somewhere.(1)
-- E
(1) But then again, I have a lot of those
> Failures from "Optional" and "throws" operate sequentially and halt
> immediately: the first "nil" or "throw" encountered prevents all work chained
> from it[1]. Another upcoming sequential operation that's worth thinking about
> in this discussion: "async"/"await".
>
> Applicative structures throw away that sequential constraint. Let's consider
> some fun things that happen when we take it away in a couple of the examples
> above.
>
> If "throws" were applicative, you could accumulate a bunch of errors at once.
>
> do {
> // made-up syntax
> let user = User(|name: try validate(name: name), email: try
> validate(email: email)|)
> } catch {
> print(error) // .manyErrors(["name is too short", "email is invalid"])
> }
>
> Currently, the above would halt on the first error.
>
> If "async"/"await" were applicative, you could fire off a bunch of
> asynchronous requests in parallel.
>
> let homepageData = HomepageData(|await fetchCurrentUser(), await
> fetchProducts()|)
>
> In the proposed version of "async"/"await", the above would block on
> "fetchCurrentUser()" and only call "fetchProducts()" after the response.
>
> "Optional" would get to use that same sugar! An example from the original
> email:
>
> getPostageEstimate(|source: john.address, destination: alice.address,
> weight 2.0|)
>
>
> --
> [1]: "Optional" and "throws" are monadic structures and "flatMap" is the
> abstraction of this sequential operation.
>
>
> Stephen
>
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