Question

I have been trying to write some code in Scala to read a file and break it into lines for the purpose of adding words to a tree structure. I have taken several different approaches to this, but all have been met with the same error:

java.lang.IndexOutOfBoundsException: -1
at scala.collection.immutable.Vector.checkRangeConvert(Vector.scala:140)
at scala.collection.immutable.Vector.apply(Vector.scala:130)
at WordTree.addWord(Main.scala:27)
at bot$$anonfun$main$2.apply(bot.scala:12)
at bot$$anonfun$main$2.apply(bot.scala:10)
at scala.collection.Iterator$class.foreach(Iterator.scala:772)
at scala.collection.Iterator$$anon$22.foreach(Iterator.scala:451)
at bot$.main(bot.scala:10)
at bot.main(bot.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at scala.tools.nsc.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:78)
at scala.tools.nsc.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:24)
at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:88)
at scala.tools.nsc.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:78)
at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:33)
at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:40)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:56)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:80)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:89)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

I’ve tried:

val wordtree = new WordTree
val wordlist = Source.fromFile("/usr/share/dict/words").getLines

for { line <- wordlist
      if (line.length > 1)
} wordtree.addWord(line)

// As well as
val wordtree = new WordTree
Source.fromFile("/usr/share/dict/words").mkString("").split("\n").foreach(
  wordtree.addWord(_))

As well as a number of variations using the elements present in each.
Is this a bug with the collections library or is there something seriously wrong with my code, here?
I’m using Scala 2.9.2 on OS X.

EDIT:
Here’s the code for the WordTree and Node.

class Node(val letter: Char, var endsWord: Boolean, var connections: List[Node] = List()) {
    def getLink(letter: Char): Node = {
        for (connection <- connections) {
            if (connection.letter == letter)
                return connection
        }
        null.asInstanceOf[Node]
    }

    def addLink(letter: Char, endsWord: Boolean) = 
        connections = (new Node(letter, endsWord)) :: connections

    def printable: String = 
        "(" + letter.toString() + "->" + connections.map(_.printable).mkString(", ") + ")"
}

class WordTree() {
    val alphabet = "abcdefghijklmnopqrstuvwxyz"
    var base = alphabet.map(c => new Node(c.asInstanceOf[Char], false))

    def addWord(word: String, n: Node = null): Node = {
        var node = n
        var link = n

        if (word.length == 0) return null.asInstanceOf[Node]
        if (n == null) node = base(alphabet.indexOf(word(0)))
        if (word.length == 1) {
            node.endsWord = true
            return node
        }
        link = node.getLink(word(1).asInstanceOf[Char])
        if (link != null) 
            return addWord(word.slice(1, word.length), link)
        node.addLink(word(1).asInstanceOf[Char], false)
        link = node.getLink(word(1).asInstanceOf[Char])
        addWord(word.slice(1, word.length), link)
    }

    def findWord(word: String, n: Node = null): Node = {
        var node = n
        var link = n

        if (n == null) node = base(alphabet.indexOf(word(0)))
        if (word.length == 1) 
            return if (node.endsWord) node else null.asInstanceOf[Node]
        link = node.getLink(word(1).asInstanceOf[Char])
        if (link != null) return findWord(word.slice(1, word.length), link)
        return null.asInstanceOf[Node]
    }
}

Answer 1

The alphabet variable is incomplete, given the words from the dictionary. The dictionary file contains words that start with uppercase letters. When you search for indexOf("A") it will return -1 because “A” does not exist in alphabet.

You can resolve this by either adding uppercase letters to alphabet, or using .toLowerCase before passing the word into addWord.