[swift-evolution] [Proposal] Higher Kinded Types (Monads, Functors, etc.)

Chris Lattner clattner at apple.com
Sun Dec 11 23:46:39 CST 2016

On Dec 11, 2016, at 5:48 AM, Elviro Rocca via swift-evolution <swift-evolution at swift.org> wrote:
> Hi everyone, I read every post in the Higher-Kinded Types ( https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002736.html <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002736.html> ) thread from about a year ago, and I was wondering what's the status on the matter: I'm aware of the proposal draft ( https://github.com/typelift/swift/issues/1 <https://github.com/typelift/swift/issues/1> ), but I'd like to know if the Swift team has reconsidered the possible relevance of HKT for Swift in the foreseeable future.

Hi Elviro,

HKT’s come up from time to time, so there is definitely interest, that said, I can’t imagine that this will be a priority to get done in Swift 4.

> By reading the discussion I found that the main concern from the Swift team was about practical use cases that could be of interest for a huge chunk of Swift developers: I don't think that a language feature should be there only if affects the majority of users, because of course you always have users at many different levels of awareness and understanding, not to mention experience and background,

Right.  I’m personally not opposed to having advanced features in Swift when they are highly motivated.  We only aim to make sure that they only affect/benefit people who want to use them.  Advanced features that beginners are forced to reckon with violate our goals to have a shallow learning curve.  HKTs seem like they’d be fine in this regard.

> but I understand that, considering the time constraints in language development and proposals review, the focus should (initially) be on things that matter the most to the vast majority of developers.

Right, this is the principle reason I can’t imagine that HKTs will get prioritized.  There are a *TON* of improvements that will have widespread positive impact, and the Swift compiler team is very thinly spread.  We are forced to pick and choose a few things that we think will have the biggest impact on the entire Swift community.


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