speedcom · October 17, 2015 19:45 · Oct 17, 2015
diff --git a/monad.scala b/monad.scala
@@ -0,0 +1,39 @@
+/** A for comprehension ready Monad */
+case class Focomo[A](value: A) {
+  self =>
+  /** satisfies monadic binding of a function f that returns B */
+  def map[B](f: A => B): Focomo[B] = { 
+    println("map!"); 
+    Focomo(f(value)) 
+  }
+  /** satisfies monadic binding of a function f that returns Focomo[B] */
+  def flatMap[B](f: A => Focomo[B]): Focomo[B] = { 
+    println("flatMap!"); 
+    f(value) 
+  }
+  /** expect this to be called in a `Unit` for comprehension */
+  def foreach[U](f: A => U): Unit = { 
+    println("foreach!"); 
+    f(value) 
+  }
+  /** for comprehension's `if` statements trigger this. 
+   *  In a more useful monad, the result of the application 
+   *  of a value to function f would determine the a special subclass
+   *  of the monad or other either-or behavior.
+   */
+  def filter(f: A => Boolean): Focomo[A] = { 
+    println("filter!"); 
+    this
+  }
+  /** provides a delegate handler for calls to #withFilter */
+  class WithFilter(p: A => Boolean) {
+    println("with filter!")
+    def map[B](f: A => B): Focomo[B] = self.filter(p).map(f)
+    def flatMap[B](f: A => Focomo[B]): Focomo[B] = self.filter(p).flatMap(f)
+    def foreach[U](f: A => U): Unit = self.filter(p).foreach(f)
+    def withFilter(q: A => Boolean): WithFilter =
+      new WithFilter(x => p(x) && q(x))
+  }
+  /** called with conditional statement in for comprehension */
+  def withFilter(p: A => Boolean): WithFilter = new WithFilter(p)
+}