Merge pull request #1 from adambard/master

update

1 files changed, 192 insertions, 85 deletions

diff --git a/scala.html.markdown b/scala.html.markdown
index 61c735e3..78053b40 100644
--- a/scala.html.markdown
+++ b/scala.html.markdown
@@ -5,53 +5,98 @@ contributors:
     - ["George Petrov", "http://github.com/petrovg"]
     - ["Dominic Bou-Samra", "http://dbousamra.github.com"]
     - ["Geoff Liu", "http://geoffliu.me"]
-filename: learn.scala
+    - ["Ha-Duong Nguyen", "http://reference-error.org"]
 ---
 
 Scala - the scalable language
 
 ```scala
 
+/////////////////////////////////////////////////
+// 0. Basics
+/////////////////////////////////////////////////
 /*
-  Set yourself up:
+  Setup Scala:
 
   1) Download Scala - http://www.scala-lang.org/downloads
-  2) unzip/untar in your favourite location and put the bin subdir on the path
-  3) Start a scala REPL by typing scala. You should see the prompt:
+  2) Unzip/untar to your favorite location and put the bin subdir in your `PATH` environment variable
+*/
 
-  scala>
+/*
+  Try the REPL
 
-  This is the so called REPL (Read-Eval-Print Loop). You may type any valid
-  Scala expression into it, and the result will be printed. We will explain what
-  Scala files look like further into this tutorial, but for now, let's start
-  with some basics.
+  Scala has a tool called the REPL (Read-Eval-Print Loop) that is analogous to
+  commandline interpreters in many other languages. You may type any Scala
+  expression, and the result will be evaluated and printed.  
+
+  The REPL is a very handy tool to test and verify code.  Use it as you read
+  this tutorial to quickly explore concepts on your own.
 */
 
+// Start a Scala REPL by running `scala`. You should see the prompt:
+$ scala
+scala>
+
+// By default each expression you type is saved as a new numbered value
+scala> 2 + 2
+res0: Int = 4
+
+// Default values can be reused.  Note the value type displayed in the result..
+scala> res0 + 2
+res1: Int = 6
+
+// Scala is a strongly typed language. You can use the REPL to check the type
+// without evaluating an expression.
+scala> :type (true, 2.0)
+(Boolean, Double)
+
+// REPL sessions can be saved
+scala> :save /sites/repl-test.scala
+
+// Files can be loaded into the REPL
+scala> :load /sites/repl-test.scala
+Loading /sites/repl-test.scala...
+res2: Int = 4
+res3: Int = 6
+
+// You can search your recent history
+scala> :h?
+1 2 + 2
+2 res0 + 2
+3 :save /sites/repl-test.scala
+4 :load /sites/repl-test.scala
+5 :h?
+
+// Now that you know how to play, let's learn a little scala...
 
 /////////////////////////////////////////////////
 // 1. Basics
 /////////////////////////////////////////////////
 
-// Single line comments start with two forward slashes
+// Single-line comments start with two forward slashes
 
 /*
-  Multi line comments, as you can already see from above, look like this.
+  Multi-line comments, as you can already see from above, look like this.
 */
 
 // Printing, and forcing a new line on the next print
 println("Hello world!")
 println(10)
+// Hello world!
+// 10
 
 // Printing, without forcing a new line on next print
 print("Hello world")
+print(10)
+// Hello world10
 
 // Declaring values is done using either var or val.
-// val declarations are immutable, whereas var's are mutable. Immutability is
+// val declarations are immutable, whereas vars are mutable. Immutability is
 // a good thing.
 val x = 10 // x is now 10
-x = 20 // error: reassignment to val
+x = 20     // error: reassignment to val
 var y = 10
-y = 20  // y is now 20
+y = 20     // y is now 20
 
 /*
   Scala is a statically typed language, yet note that in the above declarations,
@@ -71,18 +116,19 @@ true
 false
 
 // Boolean operations
-!true // false
-!false // true
+!true         // false
+!false        // true
 true == false // false
-10 > 5 // true
+10 > 5        // true
 
 // Math is as per usual
-1 + 1 // 2
-2 - 1 // 1
-5 * 3 // 15
-6 / 2 // 3
-6 / 4 // 1
+1 + 1   // 2
+2 - 1   // 1
+5 * 3   // 15
+6 / 2   // 3
+6 / 4   // 1
 6.0 / 4 // 1.5
+6 / 4.0 // 1.5
 
 
 // Evaluating an expression in the REPL gives you the type and value of the result
@@ -120,12 +166,12 @@ s"We have $n apples" // => "We have 45 apples"
 
 // Expressions inside interpolated strings are also possible
 val a = Array(11, 9, 6)
-s"My second daughter is ${a(0) - a(2)} years old." // => "My second daughter is 5 years old."
+s"My second daughter is ${a(0) - a(2)} years old."    // => "My second daughter is 5 years old."
 s"We have double the amount of ${n / 2.0} in apples." // => "We have double the amount of 22.5 in apples."
-s"Power of 2: ${math.pow(2, 2)}" // => "Power of 2: 4"
+s"Power of 2: ${math.pow(2, 2)}"                      // => "Power of 2: 4"
 
 // Formatting with interpolated strings with the prefix "f"
-f"Power of 5: ${math.pow(5, 2)}%1.0f" // "Power of 5: 25"
+f"Power of 5: ${math.pow(5, 2)}%1.0f"         // "Power of 5: 25"
 f"Square root of 122: ${math.sqrt(122)}%1.4f" // "Square root of 122: 11.0454"
 
 // Raw strings, ignoring special characters.
@@ -164,6 +210,12 @@ def sumOfSquaresShort(x: Int, y: Int): Int = x * x + y * y
 // Syntax for calling functions is familiar:
 sumOfSquares(3, 4)  // => 25
 
+// You can use parameters names to specify them in different order
+def subtract(x: Int, y: Int): Int = x - y
+
+subtract(10, 3)     // => 7
+subtract(y=10, x=3) // => -7
+
 // In most cases (with recursive functions the most notable exception), function
 // return type can be omitted, and the same type inference we saw with variables
 // will work with function return values:
@@ -171,12 +223,12 @@ def sq(x: Int) = x * x  // Compiler can guess return type is Int
 
 // Functions can have default parameters:
 def addWithDefault(x: Int, y: Int = 5) = x + y
-addWithDefault(1, 2)  // => 3
-addWithDefault(1)  // => 6
+addWithDefault(1, 2) // => 3
+addWithDefault(1)    // => 6
 
 
 // Anonymous functions look like this:
-(x:Int) => x * x
+(x: Int) => x * x
 
 // Unlike defs, even the input type of anonymous functions can be omitted if the
 // context makes it clear. Notice the type "Int => Int" which means a function
@@ -186,15 +238,15 @@ val sq: Int => Int = x => x * x
 // Anonymous functions can be called as usual:
 sq(10)   // => 100
 
-// If your anonymous function has one or two arguments, and each argument is
+// If each argument in your anonymous function is
 // used only once, Scala gives you an even shorter way to define them. These
 // anonymous functions turn out to be extremely common, as will be obvious in
 // the data structure section.
 val addOne: Int => Int = _ + 1
 val weirdSum: (Int, Int) => Int = (_ * 2 + _ * 3)
 
-addOne(5)  // => 6
-weirdSum(2, 4)  // => 16
+addOne(5)      // => 6
+weirdSum(2, 4) // => 16
 
 
 // The return keyword exists in Scala, but it only returns from the inner-most
@@ -204,9 +256,9 @@ weirdSum(2, 4)  // => 16
 def foo(x: Int): Int = {
   val anonFunc: Int => Int = { z =>
     if (z > 5)
-      return z  // This line makes z the return value of foo!
+      return z // This line makes z the return value of foo!
     else
-      z + 2  // This line is the return value of anonFunc
+      z + 2    // This line is the return value of anonFunc
   }
   anonFunc(x)  // This line is the return value of foo
 }
@@ -218,40 +270,42 @@ def foo(x: Int): Int = {
 
 1 to 5
 val r = 1 to 5
-r.foreach( println )
+r.foreach(println)
 
 r foreach println
 // NB: Scala is quite lenient when it comes to dots and brackets - study the
 // rules separately. This helps write DSLs and APIs that read like English
 
-(5 to 1 by -1) foreach ( println )
+(5 to 1 by -1) foreach (println)
 
-// A while loops
+// A while loop
 var i = 0
-while (i < 10) {  println("i " + i); i+=1  }
+while (i < 10) { println("i " + i); i += 1 }
 
-while (i < 10) {  println("i " + i); i+=1  }   // Yes, again. What happened? Why?
+while (i < 10) { println("i " + i); i += 1 }   // Yes, again. What happened? Why?
 
 i    // Show the value of i. Note that while is a loop in the classical sense -
      // it executes sequentially while changing the loop variable. while is very
-     // fast, faster that Java loops, but using the combinators and
-     // comprehensions above is easier to understand and parallelize
+     // fast, but using the combinators and comprehensions above is easier
+     // to understand and parallelize
 
-// A do while loop
+// A do-while loop
+i = 0
 do {
-  println("x is still less than 10");
-  x += 1
-} while (x < 10)
+  println("i is still less than 10")
+  i += 1
+} while (i < 10)
 
-// Tail recursion is an idiomatic way of doing recurring things in Scala.
+// Recursion is the idiomatic way of repeating an action in Scala (as in most
+// other functional languages).
 // Recursive functions need an explicit return type, the compiler can't infer it.
 // Here it's Unit.
-def showNumbersInRange(a:Int, b:Int):Unit = {
+def showNumbersInRange(a: Int, b: Int): Unit = {
   print(a)
   if (a < b)
     showNumbersInRange(a + 1, b)
 }
-showNumbersInRange(1,14)
+showNumbersInRange(1, 14)
 
 
 // Conditionals
@@ -261,7 +315,7 @@ val x = 10
 if (x == 1) println("yeah")
 if (x == 10) println("yeah")
 if (x == 11) println("yeah")
-if (x == 11) println ("yeah") else println("nay")
+if (x == 11) println("yeah") else println("nay")
 
 println(if (x == 10) "yeah" else "nope")
 val text = if (x == 10) "yeah" else "nope"
@@ -272,21 +326,21 @@ val text = if (x == 10) "yeah" else "nope"
 /////////////////////////////////////////////////
 
 val a = Array(1, 2, 3, 5, 8, 13)
-a(0)
-a(3)
+a(0)     // Int = 1
+a(3)     // Int = 5
 a(21)    // Throws an exception
 
 val m = Map("fork" -> "tenedor", "spoon" -> "cuchara", "knife" -> "cuchillo")
-m("fork")
-m("spoon")
+m("fork")         // java.lang.String = tenedor
+m("spoon")        // java.lang.String = cuchara
 m("bottle")       // Throws an exception
 
 val safeM = m.withDefaultValue("no lo se")
-safeM("bottle")
+safeM("bottle")   // java.lang.String = no lo se
 
 val s = Set(1, 3, 7)
-s(0)
-s(1)
+s(0)      // Boolean = false
+s(1)      // Boolean = true
 
 /* Look up the documentation of map here -
  * http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map
@@ -305,17 +359,24 @@ s(1)
 (a, 2, "three")
 
 // Why have this?
-val divideInts = (x:Int, y:Int) => (x / y, x % y)
+val divideInts = (x: Int, y: Int) => (x / y, x % y)
 
-divideInts(10,3) // The function divideInts gives you the result and the remainder
+// The function divideInts gives you the result and the remainder
+divideInts(10, 3)    // (Int, Int) = (3,1)
 
 // To access the elements of a tuple, use _._n where n is the 1-based index of
 // the element
-val d = divideInts(10,3)
+val d = divideInts(10, 3)    // (Int, Int) = (3,1)
+
+d._1    // Int = 3
+d._2    // Int = 1
 
-d._1
+// Alternatively you can do multiple-variable assignment to tuple, which is more
+// convenient and readable in many cases
+val (div, mod) = divideInts(10, 3)
 
-d._2
+div     // Int = 3
+mod     // Int = 1
 
 
 /////////////////////////////////////////////////
@@ -359,7 +420,7 @@ class Dog(br: String) {
 
 val mydog = new Dog("greyhound")
 println(mydog.breed) // => "greyhound"
-println(mydog.bark) // => "Woof, woof!"
+println(mydog.bark)  // => "Woof, woof!"
 
 
 // The "object" keyword creates a type AND a singleton instance of it. It is
@@ -399,8 +460,52 @@ val otherGeorge = george.copy(phoneNumber = "9876")
 
 // And many others. Case classes also get pattern matching for free, see below.
 
+// Traits
+// Similar to Java interfaces, traits define an object type and method
+// signatures. Scala allows partial implementation of those methods.
+// Constructor parameters are not allowed. Traits can inherit from other
+// traits or classes without parameters.
+
+trait Dog {
+	def breed: String
+	def color: String
+	def bark: Boolean = true
+	def bite: Boolean
+}
+class SaintBernard extends Dog {
+	val breed = "Saint Bernard"
+	val color = "brown"
+	def bite = false
+}  
+
+scala> b  
+res0: SaintBernard = SaintBernard@3e57cd70  
+scala> b.breed  
+res1: String = Saint Bernard  
+scala> b.bark  
+res2: Boolean = true  
+scala> b.bite  
+res3: Boolean = false  
+
+// A trait can also be used as Mixin. The class "extends" the first trait,
+// but the keyword "with" can add additional traits.
+
+trait Bark {
+	def bark: String = "Woof"
+}
+trait Dog {
+	def breed: String
+	def color: String
+}
+class SaintBernard extends Dog with Bark {
+	val breed = "Saint Bernard"
+	val color = "brown"
+}
 
-// Traits coming soon!
+scala> val b = new SaintBernard
+b: SaintBernard = SaintBernard@7b69c6ba
+scala> b.bark
+res0: String = Woof
 
 
 /////////////////////////////////////////////////
@@ -414,8 +519,8 @@ val otherGeorge = george.copy(phoneNumber = "9876")
 def matchPerson(person: Person): String = person match {
   // Then you specify the patterns:
   case Person("George", number) => "We found George! His number is " + number
-  case Person("Kate", number) => "We found Kate! Her number is " + number
-  case Person(name, number) => "We matched someone : " + name + ", phone : " + number
+  case Person("Kate", number)   => "We found Kate! Her number is " + number
+  case Person(name, number)     => "We matched someone : " + name + ", phone : " + number
 }
 
 val email = "(.*)@(.*)".r  // Define a regex for the next example.
@@ -446,14 +551,17 @@ def matchEverything(obj: Any): String = obj match {
   case List(1, b, c) => s"Got a list with three elements and starts with 1: 1, $b, $c"
 
   // You can nest patterns:
-  case List(List((1, 2,"YAY"))) => "Got a list of list of tuple"
+  case List(List((1, 2, "YAY"))) => "Got a list of list of tuple"
+
+  // Match any case (default) if all previous haven't matched
+  case _ => "Got unknown object"
 }
 
 // In fact, you can pattern match any object with an "unapply" method. This
 // feature is so powerful that Scala lets you define whole functions as
 // patterns:
 val patternFunc: Person => String = {
-  case Person("George", number") => s"George's number: $number"
+  case Person("George", number) => s"George's number: $number"
   case Person(name, number) => s"Random person's number: $number"
 }
 
@@ -465,6 +573,7 @@ val patternFunc: Person => String = {
 // Scala allows methods and functions to return, or take as parameters, other
 // functions or methods.
 
+val add10: Int => Int = _ + 10 // A function taking an Int and returning an Int
 List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element
 
 // Anonymous functions can be used instead of named functions:
@@ -492,7 +601,7 @@ sSquared.reduce (_+_)
 // The filter function takes a predicate (a function from A -> Boolean) and
 // selects all elements which satisfy the predicate
 List(1, 2, 3) filter (_ > 2) // List(3)
-case class Person(name:String, age:Int)
+case class Person(name: String, age: Int)
 List(
   Person(name = "Dom", age = 23),
   Person(name = "Bob", age = 30)
@@ -529,7 +638,7 @@ for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
  * best practices around them. We only include this section in the tutorial
  * because they are so commonplace in Scala libraries that it is impossible to
  * do anything meaningful without using a library that has implicits. This is
- * meant for you to understand and work with implicts, not declare your own.
+ * meant for you to understand and work with implicits, not declare your own.
  */
 
 // Any value (vals, functions, objects, etc) can be declared to be implicit by
@@ -540,8 +649,8 @@ implicit def myImplicitFunction(breed: String) = new Dog("Golden " + breed)
 
 // By itself, implicit keyword doesn't change the behavior of the value, so
 // above values can be used as usual.
-myImplicitInt + 2  // => 102
-myImplicitFunction("Pitbull").breed  // => "Golden Pitbull"
+myImplicitInt + 2                   // => 102
+myImplicitFunction("Pitbull").breed // => "Golden Pitbull"
 
 // The difference is that these values are now eligible to be used when another
 // piece of code "needs" an implicit value. One such situation is implicit
@@ -559,8 +668,8 @@ sendGreetings("Jane")  // => "Hello Jane, 100 blessings to you and yours!"
 // Implicit function parameters enable us to simulate type classes in other
 // functional languages. It is so often used that it gets its own shorthand. The
 // following two lines mean the same thing:
-def foo[T](implicit c: C[T]) = ...
-def foo[T : C] = ...
+// def foo[T](implicit c: C[T]) = ...
+// def foo[T : C] = ...
 
 
 // Another situation in which the compiler looks for an implicit is if you have
@@ -569,8 +678,8 @@ def foo[T : C] = ...
 // implicit conversion of type A => B, where A is the type of obj, and B has a
 // method called "method", that conversion is applied. So having
 // myImplicitFunction above in scope, we can say:
-"Retriever".breed  // => "Golden Retriever"
-"Sheperd".bark  // => "Woof, woof!"
+"Retriever".breed // => "Golden Retriever"
+"Sheperd".bark    // => "Woof, woof!"
 
 // Here the String is first converted to Dog using our function above, and then
 // the appropriate method is called. This is an extremely powerful feature, but
@@ -593,11 +702,14 @@ import scala.collection.immutable._
 import scala.collection.immutable.{List, Map}
 
 // Rename an import using '=>'
-import scala.collection.immutable.{ List => ImmutableList }
+import scala.collection.immutable.{List => ImmutableList}
 
 // Import all classes, except some. The following excludes Map and Set:
 import scala.collection.immutable.{Map => _, Set => _, _}
 
+// Java classes can also be imported. Scala syntax can be used
+import java.swing.{JFrame, JWindow}
+
 // Your programs entry point is defined in an scala file using an object, with a
 // single method, main:
 object Application {
@@ -628,13 +740,8 @@ writer.close()
 
 ## Further resources
 
-[Scala for the impatient](http://horstmann.com/scala/)
-
-[Twitter Scala school](http://twitter.github.io/scala_school/)
-
-[The scala documentation](http://docs.scala-lang.org/)
-
-[Try Scala in your browser](http://scalatutorials.com/tour/)
-
-Join the [Scala user group](https://groups.google.com/forum/#!forum/scala-user)
-
+* [Scala for the impatient](http://horstmann.com/scala/)
+* [Twitter Scala school](http://twitter.github.io/scala_school/)
+* [The scala documentation](http://docs.scala-lang.org/)
+* [Try Scala in your browser](http://scalatutorials.com/tour/)
+* Join the [Scala user group](https://groups.google.com/forum/#!forum/scala-user)