gistfile1.scala

val alphabet = "abcdefghijklmnopqrstuvwxyz"

def train(text:String) = {
  "[a-z]+".r.findAllIn(text).foldLeft(Map[String, Int]() withDefaultValue 1) {(a, b) => a(b) = a(b) + 1}
}

val NWORDS = train(scala.io.Source.fromFile("big.txt").getLines.mkString.toLowerCase)

def known(words:Set[String]) = {println("Known invocation: %s" format words); Set.empty ++ (for(w <- words if NWORDS contains w) yield w)}

def edits1(word:String) = {
  Set.empty ++
  (for (i <- 0 until word.length) yield (word take i) + (word drop (i + 1))) ++ // Deletes
  (for (i <- 0 until word.length - 1) yield (word take i) + word(i + 1) + word(i) + (word drop (i + 2))) ++ // Transposes
  (for (i <- 0 until word.length; j <- alphabet) yield (word take i) + j + (word drop (i+1))) ++ // Replaces
  (for (i <- 0 until word.length; j <- alphabet) yield (word take i) + j + (word drop i)) // Inserts
}

def known_edits2(word:String) = {Set.empty ++ (for (e1 <- edits1(word); e2 <- edits1(e1) if NWORDS contains e2) yield e2)}

implicit def toOr[A](one: Set[A]) = new AnyRef {
  def or(other: => Set[A]): Set[A] = { println("or called: %s" format one); if (one.isEmpty) other else one }
}

def correct(word: String) = {
  val candidates = known(Set(word)) or known(edits1(word)) or known_edits2(word) or Set(word)
  candidates.foldLeft("") {(a, b) => if (NWORDS(a) > NWORDS(b)) a else b}
}

/* Outputs:
 * scala> correct("the")
 * Known invocation: Set(the)
 * Known invocation: Set(the)
 * or called: Set(the)
 * Known invocation: Set(the)
 * Known invocation: Set(the)
 * or called: Set(the)
 * or called: Set(the)
 * Known invocation: Set(the)
 * Known invocation: Set(the)
 * or called: Set(the)
 * Known invocation: Set(the)
 * Known invocation: Set(the)
 * or called: Set(the)
 * or called: Set(the)
 * or called: Set(the)
 * res3: java.lang.String = the
 */