A huge re-organization of the Scala file

1 files changed, 193 insertions, 165 deletions

diff --git a/scala.html.markdown b/scala.html.markdown
index 5a0cc0ff..a55e1f0e 100644
--- a/scala.html.markdown
+++ b/scala.html.markdown
@@ -4,6 +4,7 @@ filename: learnscala.scala
 contributors:
     - ["George Petrov", "http://github.com/petrovg"]
     - ["Dominic Bou-Samra", "http://dbousamra.github.com"]
+    - ["Geoff Liu", "http://geoffliu.me"]
 filename: learn.scala
 ---
 
@@ -20,16 +21,16 @@ Scala - the scalable language
 
   scala>
 
-  This is the so called REPL. You can run commands in the REPL. Let's do just
-  that:
+  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.
 */
 
-println(10) // prints the integer 10
 
-println("Boo!") // printlns the string Boo!
-
-
-// Some basics
+#################################################
+## 1. Basics
+#################################################
 
 // Printing, and forcing a new line on the next print
 println("Hello world!")
@@ -37,15 +38,15 @@ println("Hello world!")
 print("Hello world")
 
 // 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 var's are mutable. Immutability is
 // a good thing.
 val x = 10 // x is now 10
 x = 20 // error: reassignment to val
-var x = 10 
+var x = 10
 x = 20  // x is now 20
 
 //  Single line comments start with two forward slashes
-/* 
+/*
 Multi line comments look like this.
 */
 
@@ -82,149 +83,83 @@ true == false // false
 */
 
 
-// Everything is an object, including a function. Type these in the REPL:
-
-7 // results in res30: Int = 7 (res30 is just a generated var name for the result)
-
-// The next line gives you a function that takes an Int and returns it squared
-(x:Int) => x * x    
-
-// You can assign this function to an identifier, like this:
-val sq = (x:Int) => x * x
-
-/* The above says this
-   
-   sq: Int => Int = <function1>	
-
-   Which means that this time we gave an explicit name to the value - sq is a
-   function that take an Int and returns Int.
-
-   sq can be executed as follows:
-*/
-
-sq(10)   // Gives you this: res33: Int = 100.
-
-// The colon explicitly defines the type of a value, in this case a function
-// taking an Int and returning an Int. 
-val add10: Int => Int = _ + 10 
-
-// Scala allows methods and functions to return, or take as parameters, other
-// functions or methods.
-
-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:
-List(1, 2, 3) map (x => x + 10)
-
-// And the underscore symbol, can be used if there is just one argument to the
-// anonymous function. It gets bound as the variable
-List(1, 2, 3) map (_ + 10)
-
-// If the anonymous block AND the function you are applying both take one
-// argument, you can even omit the underscore
-List("Dom", "Bob", "Natalia") foreach println
-
-
-
-// Data structures
-
-val a = Array(1, 2, 3, 5, 8, 13)
-a(0)
-a(3)
-a(21)    // Throws an exception
-
-val m = Map("fork" -> "tenedor", "spoon" -> "cuchara", "knife" -> "cuchillo")
-m("fork")
-m("spoon")
-m("bottle")       // Throws an exception
-
-val safeM = m.withDefaultValue("no lo se")
-safeM("bottle")
-
-val s = Set(1, 3, 7)
-s(0)
-s(1)
-
-/* Look up the documentation of map here - 
- * http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map 
- * and make sure you can read it
- */
-
-
-// Tuples
-
-(1, 2)
-
-(4, 3, 2)
-
-(1, 2, "three")
-
-(a, 2, "three")
-
-// Why have this?
-val divideInts = (x:Int, y:Int) => (x / y, x % y)
-
-divideInts(10,3) // The function divideInts gives you the result and the remainder
-
-// To access the elements of a tuple, use _._n where n is the 1-based index of
-// the element
-val d = divideInts(10,3)
-
-d._1
-
-d._2
-
+// Strings
 
+"Scala strings are surrounded by double quotes" //
+'a' // A Scala Char
+'Single quote strings don't exist' // Error
+"Strings have the usual Java methods defined on them".length
+"They also have some extra Scala methods.".reverse
 
-// Combinators
+// Seealso:  scala.collection.immutable.StringOps
 
-s.map(sq)
+println("ABCDEF".length)
+println("ABCDEF".substring(2, 6))
+println("ABCDEF".replace("C", "3"))
 
-val sSquared = s. map(sq)
+// String interpolation
+val n = 45
+println(s"We have $n apples") // => "We have 45 apples"
 
-sSquared.filter(_ < 10)
+// Expressions inside interpolated strings are also possible
+val a = Array(11, 9, 6)
+println(s"My second daughter is ${a(0) - a(2)} years old.") // => "My second daughter is 5 years old."
+println(s"We have double the amount of ${n / 2.0} in apples.") // => "We have double the amount of 22.5 in apples."
+println(s"Power of 2: ${math.pow(2, 2)}") // => "Power of 2: 4"
 
-sSquared.reduce (_+_)
+// Formatting with interpolated strings (note the prefixed f)
+println(f"Power of 5: ${math.pow(5, 2)}%1.0f") // "Power of 5: 25"
+println(f"Square root of 122: ${math.sqrt(122)}%1.4f") // "Square root of 122"
 
-// 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)
-List(
-  Person(name = "Dom", age = 23), 
-  Person(name = "Bob", age = 30)
-).filter(_.age > 25) // List(Person("Bob", 30))
+// Ignoring special characters.
+println(raw"New line feed: \n. Carriage return: \r.") // => "New line feed: \n. Carriage return: \r."
 
+// Some characters need to be 'escaped', e.g. a double quote inside a string:
+val a = "They stood outside the \"Rose and Crown\"" // => "They stood outside the "Rose and Crown""
 
-// Scala a foreach method defined on certain collections that takes a type
-// returning Unit (a void method)
-aListOfNumbers foreach (x => println(x))
-aListOfNumbers foreach println
+// Triple double-quotes let strings span multiple rows and contain quotes
+val html = """<form id="daform">
+                <p>Press belo', Joe</p>
+             |  <input type="submit">
+              </form>"""
 
 
+#################################################
+## 2. Functions
+#################################################
 
+// The next line gives you a function that takes an Int and returns it squared
+(x:Int) => x * x
 
-// For comprehensions
+// You can assign this function to an identifier, like this:
+val sq = (x:Int) => x * x
 
-for { n <- s } yield sq(n)
+/* The above says this
 
-val nSquared2 = for { n <- s } yield sq(n)
+   sq: Int => Int = <function1>
 
-for { n <- nSquared2 if n < 10 } yield n
+   Which means that this time we gave an explicit name to the value - sq is a
+   function that take an Int and returns Int.
 
-for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
+   sq can be executed as follows:
+*/
 
-/* NB Those were not for loops. The semantics of a for loop is 'repeat', whereas
-   a for-comprehension defines a relationship between two sets of data. */
+sq(10)   // Gives you this: res33: Int = 100.
 
+// The colon explicitly defines the type of a value, in this case a function
+// taking an Int and returning an Int.
+val add10: Int => Int = _ + 10
 
 
-// Loops and iteration
+#################################################
+## 3. Flow Control
+#################################################
 
 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
 
@@ -243,7 +178,7 @@ i    // Show the value of i. Note that while is a loop in the classical sense -
 
 // A do while loop
 do {
-  println("x is still less than 10"); 
+  println("x is still less than 10");
   x += 1
 } while (x < 10)
 
@@ -257,7 +192,6 @@ def showNumbersInRange(a:Int, b:Int):Unit = {
 }
 
 
-
 // Conditionals
 
 val x = 10
@@ -274,10 +208,76 @@ var i = 0
 while (i < 10) { println("i " + i); i+=1  }
 
 
+#################################################
+## 4. Data Structures
+#################################################
 
-// Object oriented features
+val a = Array(1, 2, 3, 5, 8, 13)
+a(0)
+a(3)
+a(21)    // Throws an exception
+
+val m = Map("fork" -> "tenedor", "spoon" -> "cuchara", "knife" -> "cuchillo")
+m("fork")
+m("spoon")
+m("bottle")       // Throws an exception
+
+val safeM = m.withDefaultValue("no lo se")
+safeM("bottle")
+
+val s = Set(1, 3, 7)
+s(0)
+s(1)
+
+/* Look up the documentation of map here -
+ * http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map
+ * and make sure you can read it
+ */
+
+
+// Tuples
+
+(1, 2)
+
+(4, 3, 2)
+
+(1, 2, "three")
+
+(a, 2, "three")
+
+// Why have this?
+val divideInts = (x:Int, y:Int) => (x / y, x % y)
+
+divideInts(10,3) // The function divideInts gives you the result and the remainder
+
+// To access the elements of a tuple, use _._n where n is the 1-based index of
+// the element
+val d = divideInts(10,3)
+
+d._1
+
+d._2
+
+
+#################################################
+## 5. Object Oriented Programming
+#################################################
+
+/*
+  Aside: Everything we've done so far in this tutorial has been simple
+  expressions (values, functions, etc). These expressions are fine to type into
+  the command-line interpreter for quick tests, but they cannot exist by
+  themselves in a Scala file. For example, you cannot have just "val x = 5" in
+  a Scala file. Instead, the only top-level constructs allowed in Scala are:
+
+  - objects
+  - classes
+  - case classes
+  - traits
+
+  And now we will explain what these are.
+*/
 
-// Classname is Dog
 class Dog {
   //A method called bark, returning a String
   def bark: String = {
@@ -289,8 +289,6 @@ class Dog {
 // Classes can contain nearly any other construct, including other classes,
 // functions, methods, objects, case classes, traits etc.
 
-
-
 // Case classes
 
 case class Person(name:String, phoneNumber:String)
@@ -298,8 +296,12 @@ case class Person(name:String, phoneNumber:String)
 Person("George", "1234") == Person("Kate", "1236")
 
 
+// Objects and traits coming soon!
+
 
-// Pattern matching
+#################################################
+## 6. Pattern Matching
+#################################################
 
 val me = Person("George", "1234")
 
@@ -338,49 +340,75 @@ matcher("52917") // => "No match on '52917'"
 matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917"
 
 
-// Strings
+#################################################
+## 7. Functional Programming
+#################################################
 
-"Scala strings are surrounded by double quotes" //
-'a' // A Scala Char
-'Single quote strings don't exist' // Error
-"Strings have the usual Java methods defined on them".length
-"They also have some extra Scala methods.".reverse
+// Scala allows methods and functions to return, or take as parameters, other
+// functions or methods.
 
-// Seealso:  scala.collection.immutable.StringOps
+List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element
 
-println("ABCDEF".length)
-println("ABCDEF".substring(2, 6))
-println("ABCDEF".replace("C", "3"))
+// Anonymous functions can be used instead of named functions:
+List(1, 2, 3) map (x => x + 10)
 
-// String interpolation
-val n = 45
-println(s"We have $n apples") // => "We have 45 apples"
+// And the underscore symbol, can be used if there is just one argument to the
+// anonymous function. It gets bound as the variable
+List(1, 2, 3) map (_ + 10)
 
-// Expressions inside interpolated strings are also possible
-val a = Array(11, 9, 6)
-println(s"My second daughter is ${a(0) - a(2)} years old.") // => "My second daughter is 5 years old."
-println(s"We have double the amount of ${n / 2.0} in apples.") // => "We have double the amount of 22.5 in apples."
-println(s"Power of 2: ${math.pow(2, 2)}") // => "Power of 2: 4"
+// If the anonymous block AND the function you are applying both take one
+// argument, you can even omit the underscore
+List("Dom", "Bob", "Natalia") foreach println
 
-// Formatting with interpolated strings (note the prefixed f)
-println(f"Power of 5: ${math.pow(5, 2)}%1.0f") // "Power of 5: 25"
-println(f"Square root of 122: ${math.sqrt(122)}%1.4f") // "Square root of 122"
 
-// Ignoring special characters.
-println(raw"New line feed: \n. Carriage return: \r.") // => "New line feed: \n. Carriage return: \r."
+// Combinators
 
-// Some characters need to be 'escaped', e.g. a double quote inside a string:
-val a = "They stood outside the \"Rose and Crown\"" // => "They stood outside the "Rose and Crown""
+s.map(sq)
 
-// Triple double-quotes let strings span multiple rows and contain quotes
-val html = """<form id="daform">
-                <p>Press belo', Joe</p>
-             |  <input type="submit">
-              </form>"""
+val sSquared = s. map(sq)
+
+sSquared.filter(_ < 10)
+
+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)
+List(
+  Person(name = "Dom", age = 23),
+  Person(name = "Bob", age = 30)
+).filter(_.age > 25) // List(Person("Bob", 30))
+
+
+// Scala a foreach method defined on certain collections that takes a type
+// returning Unit (a void method)
+aListOfNumbers foreach (x => println(x))
+aListOfNumbers foreach println
+
+// For comprehensions
+
+for { n <- s } yield sq(n)
+
+val nSquared2 = for { n <- s } yield sq(n)
+
+for { n <- nSquared2 if n < 10 } yield n
+
+for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
+
+/* NB Those were not for loops. The semantics of a for loop is 'repeat', whereas
+   a for-comprehension defines a relationship between two sets of data. */
+
+
+#################################################
+## 8. Implicits
+#################################################
 
+Coming soon!
 
 
-// Application structure and organization
+#################################################
+## 9. Misc
+#################################################
 
 // Importing things
 import scala.collection.immutable.List