added lesson 5

README.md

@@ -14,6 +14,7 @@
     * [Lesson 2 - Higher order functions](#lesson-2---higher-order-functions)
     * [Lesson 3 - Data structures](#lesson-3---data-structures)
     * [Lesson 4 - Lists and pattern matching](#lesson-4---lists-and-pattern-matching)
+    * [Lesson 5 - Advanced lists and High order functions](#lesson-5---advanced-lists-and-high-order-functions)
   * [Assignments](#assignments)
     * [Assignment 1 - Square root](#assignment-1---square-root)
     * [Assignment 2 - Map-reduce](#assignment-2---map-reduce)
@@ -49,6 +50,11 @@
 - Pattern matching
 - Genericity
 
+### Lesson 5 - Advanced lists and High order functions
+[Files](src/Lesson5)
+- Lists
+- High order functions
+
 ## Assignments
 
 ### Assignment 1 - Square root
@@ -74,4 +80,4 @@
 - Expression interpreter
 - Binary tree
 - List functions
-- Predicates (any / every)
+- Predicates (any / every)

src/Lesson5/Ex5_2.sc

@@ -0,0 +1,19 @@
+def length[A](x: List[A]): Int = {
+  x.foldRight(0)((elem: A, len: Int) => len + 1)
+}
+
+def map[A, B](x: List[A], f: A => B): List[B] = {
+  x.foldRight(List.empty[B])((elem: A, list: List[B]) => f(elem)::list)
+}
+
+def dup[A](l: List[A]): List[A] = {
+  l.flatMap(e => List(e, e))
+}
+
+def dup2[A](l: List[A]): List[A] = {
+  l.foldRight(List.empty[A])((e, l) => e::e::l)
+}
+
+length(1::2::3::4::Nil)
+map(1::2::3::4::Nil, (x: Int) => x * 2)
+dup(1::2::3::Nil)