Initial data commit

Task/Abstract-type/F-Sharp/abstract-type-1.fs

@@ -0,0 +1,8 @@
+type Shape =
+  abstract Perimeter: unit -> float
+  abstract Area: unit -> float
+
+type Rectangle(width, height) =
+  interface Shape with
+    member x.Perimeter() = 2.0 * width + 2.0 * height
+    member x.Area() = width * height

Task/Abstract-type/F-Sharp/abstract-type-2.fs

@@ -0,0 +1,16 @@
+[<AbstractClass>]
+type Bird() =
+  // an abstract (=virtual) method with default impl.
+  abstract Move : unit -> unit
+  default x.Move() = printfn "flying"
+  // a pure virtual method
+  abstract Sing: unit -> string
+
+type Blackbird() =
+  inherit Bird()
+  override x.Sing() = "tra-la-la"
+
+type Ostrich() =
+  inherit Bird()
+  override x.Move() = printfn "walking"
+  override x.Sing() = "hiss hiss!"