cc @rudkx, @xedin

@swift-ci create

FWIW it appears to be the point-free style causing issues. This works:

-return fs.flatMap { f in xs.map(f) }
+return fs.flatMap { f in xs.map { x in f(x) } }

Also broken:

return fs.flatMap(xs.map)

See also:

https://bugs.swift.org/browse/SR-5422

Another thing that fails, but shouldn't:

public extension Sequence {
  public func apply<S: Sequence, A>(_ fs: S) -> [A] where S.Element == ((Element) -> A) {
    return fs.flatMap { f in self.map { x in f(x) } }
  }

  public static func <*> <S: Sequence, A>(fs: S, xs: Self) -> [A] where S.Element == ((Element) -> A) {
    return xs.apply(fs)
    // Generic parameter 'A' could not be inferred
  }
}

public func apply<S: Sequence, T: Sequence, A>(_ fs: S) -> (T) -> [A] where S.Element == ((T.Element) -> A) {
  return { xs in
    fs <*> xs
    // Type of expression is ambiguous without more context
  }
}

Portion of SE-0110 has been rolled back via #10414 so the code from description compiles just fine now.

@stephencelis Please verify and move to closed.

All of these issues (the main one and those listed in my follow-up comment) still persist in Xcode 9 beta 4.

@stephencelis Interesting, the code in the description and in the follow-up compiles just fine with master branch, maybe some of the changes related to this didn't make it to Beta 4, I'll double check and let you know!

@stephencelis I found that your original example is fixed in Xcode 9 beta 3 and Xcode 9 beta 4.

The follow-on examples work with the nightly from 'master' but not with the nightly from 'swift-4.0-branch.'

@rudkx Checked on the latest snapshot and everything is fixed in the latest snapshot except for:

public extension Sequence {
  public func apply<S: Sequence, A>(_ fs: S) -> [A] where S.Element == ((Element) -> A) {
    return fs.flatMap(self.map)
  }
}

Call can throw, but it is not marked with 'try' and the error is not handled

Related issue: https://bugs.swift.org/browse/SR-5586

Thanks!

This one remaining issue is just a dup of the other issue, so I'm going to close this out.