Tutorial on classes and functions added

TODO: more on indexers, check the comment emitted twice for f2 function

typescript.html.markdown

@@ -6,11 +6,11 @@ contributors:
 
 TypeScript is a language that aims at easing development of large scale applications written in JavaScript.
 TypeScript adds common concepts such as classes, modules, interfaces, generics and (optional) static typing to JavaScript.
-It is a superset of JavaScript: all JavaScript code is valid TypeScript code so it can be added seamlessly to any project. In turn, the TypeScript compiler transform the code to JavaScript.
+It is a superset of JavaScript: all JavaScript code is valid TypeScript code so it can be added seamlessly to any project. The TypeScript compiler emitts JavaScript.
 
-This article will focus only on TypeScript added syntax, everything else is plain [JavaScript] (../javascript/).
+This article will focus only on TypeScript extra syntax, as oposed to [JavaScript] (../javascript/).
 
-To test TypeScript's compiler, head to the [Playground] (http://www.typescriptlang.org/Playground) where you will be able to type code, have auto completion and directly see the resulting JavaScript.
+To test TypeScript's compiler, head to the [Playground] (http://www.typescriptlang.org/Playground) where you will be able to type code, have auto completion and directly see the emitted JavaScript.
 
 ```ts
 //There are 3 basic types in TypeScript
@@ -25,10 +25,10 @@ notSure = false; // okay, definitely a boolean
 
 //For collections, there are typed arrays and generic arrays
 var list: number[] = [1, 2, 3];
-//Or, using the generic array type
+//Alternatively, using the generic array type
 var list: Array<number> = [1, 2, 3];
 
-//For enumerations
+//For enumerations:
 enum Color {Red, Green, Blue};
 var c: Color = Color.Green;
 
@@ -37,40 +37,76 @@ function bigHorribleAlert(): void {
   alert("I'm a little annoying box!");
 }
 
-//Interfaces are structural, anything that has the properties is compliant with the interface.
-//In the bellow example, any object that has a name which is a string and an age which is a number is a Person.
-//This is called "duck typing".
+//Functions are first class citizens, have a shortened definition and can leverage the strong type inference
+//All examples are equivalent, the same signature will be infered by the compiler and the same JavaScript will be emitted
+var f1 = function(i: number) : number { return i * i; }
+var f2 = function(i: number) { return i * i; } //Return type infered #TODO bug!
+var f3 = (i : number) : number => { return i * i; }
+var f4 = (i: number) => { return i * i; } //Return type infered
+var f5 = (i: number) =>  i * i; //Return type infered, one-liner means no return keyword needed
+
+//Interfaces are structural, anything that has the properties is compliant with the interface (duck typing)
 interface Person {
   name: string;
-  age: number;
-  
-  //Interfaces also support optional properties
-  phone?: number;
+  //Optional properties, marked with a "?"
+  age?: number;
+}
+//Object that implements the "Person" interface
+var p : Person = { name: "Bobby" }; //Can be treated as a Person since it has the name and age properties
+//Objects that have the optional property:
+var validPerson : Person = { name: "Bobby", age: 42 };
+var invalidPerson : Person = { name: "Bobby", age: true }; //Is not a person because age is not a number
+
+//Interfaces can also define method signatures:
+interface PersonWhoCanTalk {
+  sayHello(otherPersonsName: string): void;
 }
 
-//Interfaces can also describe a function type, to describe a function signature
+//And also indexers, both with number and string
+interface PersonWhoCanBeIndexed {
+  [index: number]: string;
+}
+//TODO
+
+//Interfaces can also describe a function type
 interface SearchFunc {
   (source: string, subString: string): boolean;
 }
-//The type can then be used for functions, and the compiler will be able to check that types are compliants
-//Note that only the parameters' types are important, names are not important.
+//Only the parameters' types are important, names are not important.
 var mySearch: SearchFunc;
 mySearch = function(src: string, sub: string) {
-  var result = source.search(subString);
-  if (result == -1) {
-    return false;
-  }
-  else {
-    return true;
-  }
+  return src.search(sub) != -1;
 }
 
+//Classes
+class Point {
+  //Properties
+	x: number;
+	
+	//Constructor - the public keyword is a shortcut to generate the code for a property and it's initialization, equivalent to "x" in this case
+	constructor(x: number, public y: number) {
+		this.x = x;
+	}
+	
+	//Functions
+	dist() { return Math.sqrt(this.x * this.x + this.y * this.y); }
+	
+	//Static members
+	static origin = new Point(0, 0);
+}
+
+var p = new Point(10 ,20);
+
+//Generics
+
+//Including references to a definition file
+/// <reference path="jquery.d.ts" />
 
 ```
 
-
-
 ## Further Reading
  * [TypeScript Official website] (http://www.typescriptlang.org/)
  * [TypeScript language specifications (pdf)] (http://go.microsoft.com/fwlink/?LinkId=267238)
  * [Anders Hejlsberg - Introducing TypeScript on Channel 9] (http://channel9.msdn.com/posts/Anders-Hejlsberg-Introducing-TypeScript)
+ * [Source Code on GitHub] (https://github.com/Microsoft/TypeScript)
+ * [Definitely Typed - repository for type definitions] (http://definitelytyped.org/)