Finish partial functions and function composition

Author: matterche

src/main/worksheets/f_Functions/d_partial_functions.sc

@@ -0,0 +1,48 @@
+/**
+ * A partial function in mathematics is only defined for a subset of the possible
+ * values of its arguments.
+ *
+ * https://en.wikipedia.org/wiki/Partial_function
+ */
+def fraction(d: Int) = 42 / d
+
+/**
+ * Scala supports definition of partial functions by a special type [[PartialFunction]]
+ */
+object Routes extends PartialFunction[String, String] {
+  override def isDefinedAt(route: String): Boolean = Seq("/hello", "/status") contains route
+
+  override def apply(route: String): String = route match {
+    case "/hello" => "Hello World"
+    case "/status" => "Alive"
+    case _ => "404"
+  }
+}
+
+Routes("/hello")
+Routes.isDefinedAt("/status")
+Routes.isDefinedAt("/alive")
+
+// Audience: What happens...
+// Routes("/alive")
+
+
+// syntactic sugar
+val dump: PartialFunction[Int, Int] = {
+  case i if i % 2 == 0 => i + 1
+}
+
+/**
+ * Partial functions can be used everywhere a function is expected
+ */
+// Audience what would you expect?
+// 0 to 10 map dump
+
+// Audience what would you expect?
+// 0 to 10 collect dump
+
+
+
+
+
+

src/main/worksheets/f_Functions/e_function_composition.sc

@@ -0,0 +1,44 @@
+/**
+ * Functions can be composed in several ways
+ */
+val times2: Int => Int = _ * 2
+val plus3: Int => Int = _ + 3
+
+
+(times2 andThen plus3)(3) == plus3(times2(3))
+
+Function.chain(Seq(times2, plus3))(3) == plus3(times2(3))
+
+(times2 compose plus3)(3) == times2(plus3(3))
+
+/**
+ * In addition, PartialFunctions can be composed via [[PartialFunction.orElse]]
+ */
+val okHandler: PartialFunction[Int, String] = {
+  case 200 => "Do some cool stuff"
+}
+
+val unauthorizedHandler: PartialFunction[Int, String] = {
+  case 401 => "Login again"
+}
+
+val paymentRequiredHandler: PartialFunction[Int, String] = {
+  case 402 => "Pay the bills"
+}
+
+val errorHandler: PartialFunction[Int, String] = {
+  case 500 => "Server Error"
+}
+
+val unknownHandler: PartialFunction[Int, String] = {
+  case _ => "Just panic"
+}
+
+def processResponse(status: Int, handler: Int => String): String = handler(status)
+
+processResponse(200, okHandler orElse errorHandler)
+processResponse(500, okHandler orElse errorHandler)
+processResponse(5, okHandler orElse errorHandler orElse unknownHandler)
+
+// Audience: What would you expect
+//processResponse(5, okHandler orElse errorHandler )