--- a/progs/lecture3.scala	Tue Nov 19 00:40:27 2019 +0000
+++ b/progs/lecture3.scala	Tue Nov 19 06:38:10 2019 +0000
@@ -47,7 +47,8 @@
   if (n == 0) ()
   else {
     println(s"  Visiting: $n $url")
-    for (u <- get_all_URLs(get_page(url))) crawl(u, n - 1)
+    val page = get_page(url)
+    for (u <- get_all_URLs(page)) crawl(u, n - 1)
   }
 }
 
@@ -121,8 +122,9 @@
 
 def search(xs: List[Int]) : Boolean = xs match {
   case Nil => true
-  case (x::xs) =>
-    if (xs.length < x) true else moves(xs, x).exists(search(_))
+  case x::xs =>
+    if (xs.length < x) true 
+    else moves(xs, x).exists(search(_))
 }
 
 
@@ -138,7 +140,7 @@
 search(List(3,5,1,0,0,0,0,0,0,0,0,1))
 
 // generates *all* jump tours
-//    if we are only interested in the shortes one, we could
+//    if we are only interested in the shortest one, we could
 //    shortcircut the calculation and only return List(x) in
 //    case where xs.length < x, because no tour can be shorter
 //    than 1
@@ -146,7 +148,7 @@
 
 def jumps(xs: List[Int]) : List[List[Int]] = xs match {
   case Nil => Nil
-  case (x::xs) => {
+  case x::xs => {
     val children = moves(xs, x)
     val results = children.map(cs => jumps(cs).map(x :: _)).flatten
     if (xs.length < x) List(x)::results else results
@@ -180,7 +182,7 @@
 //========================
 
 
-abstract class Colour
+sealed abstract class Colour
 case object Red extends Colour 
 case object Green extends Colour 
 case object Blue extends Colour
@@ -196,7 +198,7 @@
 
 // ... a tiny bit more useful: Roman Numerals
 
-abstract class RomanDigit 
+sealed abstract class RomanDigit 
 case object I extends RomanDigit 
 case object V extends RomanDigit 
 case object X extends RomanDigit 
@@ -269,7 +271,7 @@
 
 // trees
 
-abstract class Exp
+sealed abstract class Exp
 case class N(n: Int) extends Exp                  // for numbers
 case class Plus(e1: Exp, e2: Exp) extends Exp
 case class Times(e1: Exp, e2: Exp) extends Exp
@@ -314,7 +316,7 @@
 
 
 // Tokens and Reverse Polish Notation
-abstract class Token
+sealed abstract class Token
 case class T(n: Int) extends Token
 case object PL extends Token
 case object TI extends Token

--- a/progs/sudoku.scala	Tue Nov 19 00:40:27 2019 +0000
+++ b/progs/sudoku.scala	Tue Nov 19 06:38:10 2019 +0000
@@ -56,11 +56,9 @@
 // a list of hard games according to Andrew Coles and Peter Norvig
 
 val hard_games = 
-  List("4.....8.5.3..........7......2.....6.....8.4......1.......6.3.7.5..2.....1.4......",
-       "52...6.........7.13...........4..8..6......5...........418.........3..2...87.....",
+  List("52...6.........7.13...........4..8..6......5...........418.........3..2...87.....",
        "6.....8.3.4.7.................5.4.7.3..2.....1.6.......2.....5.....8.6......1....",
        "48.3............71.2.......7.5....6....2..8.............1.76...3.....4......5....",
-       "....14....3....2...7..........9...3.6.1.............8.2.....1.4....5.6.....7.8...",
        "......52..8.4......3...9...5.1...6..2..7........3.....6...1..........7.4.......3.",
        "6.2.5.........3.4..........43...8....1....2........7..5..27...........81...6.....",
        ".524.........7.1..............8.2...3.....6...9.5.....1.6.3...........897........",
@@ -167,7 +165,9 @@
        ".2.3.......6..8.9.83.5........2...8.7.9..5........6..4.......1...1...4.22..7..8.9",
        ".5..9....1.....6.....3.8.....8.4...9514.......3....2..........4.8...6..77..15..6.",
        ".....2.......7...17..3...9.8..7......2.89.6...13..6....9..5.824.....891..........",
-       "3...8.......7....51..............36...2..4....7...........6.13..452...........8..")
+       "3...8.......7....51..............36...2..4....7...........6.13..452...........8..",
+       "....14....3....2...7..........9...3.6.1.............8.2.....1.4....5.6.....7.8...",
+       "4.....8.5.3..........7......2.....6.....8.4......1.......6.3.7.5..2.....1.4......")
 
 
 // for measuring time