eliminating a mutable buffer

buffer.scala

import java.io._

def userStream =
  new BufferedReader(
    new InputStreamReader(
      new FileInputStream("/etc/passwd")))

// imperative style
def linesI(s: BufferedReader): List[String] = {
  val buf = new collection.mutable.ListBuffer[String]
  while(true) {
    val line = s.readLine()
    if(line == null)
      return buf.toList
    buf += line
  }
  error("wtf")
}

// functional style
def linesF(s: BufferedReader): List[String] =
  Iterator.continually(s.readLine()).takeWhile(_ != null).toList

linesI(userStream).foreach(println)
linesF(userStream).foreach(println)