Extending Swift's sequence

extension_sequence.swift

extension Sequence {
  func take(_ n: Int ) -> [Self.Element] {
    // yield the first n elements of a sequence as an array 
    var ret = [Self.Element]()
    
    for ( _, e) in zip( 0..<n, self ) {
      ret.append(e)
    }
    return ret
  }
}