Auto suggester

AutoSuggest.scala

class AutoSuggest(corpus: String, alphabet: Seq[Char] = 'a' to 'z', depth: Int = 2) {
  val words = s"[${alphabet.head}-${alphabet.last}]+".r
    .findAllIn(corpus.toLowerCase).toSeq
    .groupBy(_.toSeq).mapValues(_.size)
    .par withDefaultValue 0

  def editDistance(a: Seq[Char], b: Seq[Char]) = {
    lazy val d: Stream[Stream[Int]] = Stream.tabulate(a.length + 1, b.length + 1) {
      case (i, j) if (i - j).abs > depth => Int.MaxValue
      case (i, 0) => i
      case (0, j) => j
      case (i, j) if a(i-1) == b(j-1) => d(i-1)(j-1)
      case (i, j) => 1 + (d(i)(j-1) min d(i-1)(j) min d(i-1)(j-1))
    }
    d(a.length)(b.length)
  }

  def apply(word: String) = words maxBy {case (i, frequency) => -editDistance(i, word) -> frequency}
}
// Demo:
object AutoSuggest extends App {
  val suggest = new AutoSuggest(io.Source.fromFile("big.txt").mkString)  // curl http://norvig.com/big.txt > big.txt
  Seq("speling", "korrecter", "corrected", "xyz") foreach {w => println(s"$w: ${suggest(w)}")}
}