partial count(where:)

gistfile1.txt

extension Sequence {
  func count(where p: (Element)->Bool)->Int {
    return reduce(0) { p($1) ? $0 + 1 : $0 }
  }
}

let fn:  ((Int) -> Bool) -> Int = [1,2,3].count
let n = fn { $0<2 }
print(n) // 1