1.1 --- a/src/Pure/General/scan.scala	Thu Jun 18 14:02:47 2009 +0200
     1.2 +++ b/src/Pure/General/scan.scala	Thu Jun 18 15:02:18 2009 +0200
     1.3 @@ -148,7 +148,10 @@
     1.4  
     1.5      def length: Int = end - start
     1.6      def charAt(i: Int): Char = text.charAt(end - i - 1)
     1.7 -    def subSequence(i: Int, j: Int): CharSequence = new Reverse(text, end - j, end - i)
     1.8 +
     1.9 +    def subSequence(i: Int, j: Int): CharSequence =
    1.10 +      if (0 <= i && i <= j && j <= length) new Reverse(text, end - j, end - i)
    1.11 +      else throw new IndexOutOfBoundsException
    1.12  
    1.13      override def toString: String =
    1.14      {