Imperative solution to the Python indentation problem

ImperativeIndentationCheck.scala

import scala.io.Source
import scala.collection.mutable

object ImperativeIndentationCheck {

  def isValid(filename: String): Boolean = isValid(Source.fromFile(filename).getLines.toSeq)
  
  def isValid(lines: Seq[String]): Boolean = {
	  val scopes = mutable.Stack(0)
	  for(line <- lines) {
	    val i = indentationOf(line)
	    if (i > scopes.head) {
	      scopes.push(i)
	    } else while (i != scopes.head) {
	      scopes.pop()
	      if (scopes.isEmpty) return false
	    }
	  }
	  return true
  }
  
  private def indentationOf(line: String) = line.takeWhile(_.isWhitespace).size
}