added Tony's exercieses for beginners

exercises_for_beginners.scala

@@ -0,0 +1,98 @@
+// You are not permitted to use these List methods:
+// * length
+// * map
+// * filter
+// * ::: (and variations such as ++)
+// * flatten
+// * flatMap
+// * reverse (and variations i.e. reverseMap, reverse_:::)
+// This also means you are not permitted to use for-comprehensions on Lists.
+// You are permitted to use the functions you write yourself. For example, Exercise 2 may use Exercise 1 or Exercise 3.
+// Using permitted existing methods where appropriate will attract marks for elegance.
+
+// TOTAL marks:    /66
+
+object Exercises {
+  def succ(n: Int) = n + 1
+  def pred(n: Int) = n - 1
+
+  // Exercise 1
+  // Relative Difficulty: 1
+  // Correctness: 2.0 marks
+  // Performance: 0.5 mark
+  // Elegance: 0.5 marks
+  // Total: 3
+  def add(x: Int, y: Int): Int = if(y>0) add(succ(x),pred(y)) else x
+
+  // Exercise 2
+  // Relative Difficulty: 2
+  // Correctness: 2.5 marks
+  // Performance: 1 mark
+  // Elegance: 0.5 marks
+  // Total: 4
+  def sum(x: List[Int]): Int = error("todo")
+
+  // Exercise 3
+  // Relative Difficulty: 2
+  // Correctness: 2.5 marks
+  // Performance: 1 mark
+  // Elegance: 0.5 marks
+  // Total: 4
+  def length[A](x: List[A]): Int = error("todo")
+
+  // Exercise 4
+  // Relative Difficulty: 5
+  // Correctness: 4.5 marks
+  // Performance: 1.0 mark
+  // Elegance: 1.5 marks
+  // Total: 7
+  def map[A, B](x: List[A], f: A => B): List[B] = error("todo")
+
+  // Exercise 5
+  // Relative Difficulty: 5
+  // Correctness: 4.5 marks
+  // Performance: 1.5 marks
+  // Elegance: 1 mark
+  // Total: 7
+  def filter[A](x: List[A], f: A => Boolean): List[A] = error("todo")
+
+  // Exercise 6
+  // Relative Difficulty: 5
+  // Correctness: 4.5 marks
+  // Performance: 1.5 marks
+  // Elegance: 1 mark
+  // Total: 7
+  def append[A](x: List[A], y: List[A]): List[A] = error("todo")
+
+  // Exercise 7
+  // Relative Difficulty: 5
+  // Correctness: 4.5 marks
+  // Performance: 1.5 marks
+  // Elegance: 1 mark
+  // Total: 7
+  def concat[A](x: List[List[A]]): List[A] = error("todo")
+
+  // Exercise 8
+  // Relative Difficulty: 7
+  // Correctness: 5.0 marks
+  // Performance: 1.5 marks
+  // Elegance: 1.5 mark
+  // Total: 8
+  def concatMap[A, B](x: List[A], f: A => List[B]): List[B] = error("todo")
+
+  // Exercise 9
+  // Relative Difficulty: 8
+  // Correctness: 3.5 marks
+  // Performance: 3.0 marks
+  // Elegance: 2.5 marks
+  // Total: 9
+  def maximum(x: List[Int]): Int = error("todo")
+
+  // Exercise 10
+  // Relative Difficulty: 10
+  // Correctness: 5.0 marks
+  // Performance: 2.5 marks
+  // Elegance: 2.5 marks
+  // Total: 10
+  def reverse[A](x: List[A]): List[A] = error("todo")
+}