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-rw-r--r--scala.html.markdown139
1 files changed, 134 insertions, 5 deletions
diff --git a/scala.html.markdown b/scala.html.markdown
index 8bcb5975..8e00f135 100644
--- a/scala.html.markdown
+++ b/scala.html.markdown
@@ -2,6 +2,7 @@
language: Scala
contributors:
- ["George Petrov", "http://github.com/petrovg"]
+ - ["Dominic Bou-Samra, "http://dbousamra.github.com"]
filename: learn.scala
---
@@ -28,7 +29,43 @@ println(10) // prints the integer 10
println("Boo!") // printlns the string Boo!
-// Evaluating a command gives you the type and value of the result
+// Some basics
+
+// Printing, and forcing a new line on the next print
+println("Hello world!")
+// Printing, without forcing a new line on next print
+print("Hello world")
+
+// Declaring values is done using either var or val
+// val declarations are immutable, whereas var's are mutable. Immutablility is a good thing.
+val x = 10 // x is now 10
+x = 20 // error: reassignment to val
+var x = 10
+x = 20 // x is now 20
+
+// Single line comments start with two forward slashes
+/*
+Multi line comments look like this.
+*/
+
+// Boolean values
+true
+false
+
+// Boolean operations
+!true // false
+!false // true
+true == false // false
+10 > 5 // true
+
+// Math is as per usual
+1 + 1 // 2
+2 - 1 // 1
+5 * 3 // 15
+6 / 2 // 3
+
+
+// Evaluating a command in the REPL gives you the type and value of the result
1 + 7
@@ -64,6 +101,20 @@ val sq = (x:Int) => x * x
sq(10) // Gives you this: res33: Int = 100. The result is the Int with a value 100
+// 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:
+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)
+
+TODO // 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
@@ -124,6 +175,20 @@ 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
@@ -152,6 +217,7 @@ r foreach println
(5 to 1 by -1) foreach ( println )
+// A while loops
var i = 0
while (i < 10) { println("i " + i); i+=1 }
@@ -162,8 +228,14 @@ i // Show the value of i. Note that while is a loop in the classical sense -
// loops, but using the combinators and comprehensions above is easier to understand
// and parallelize
-// Tail recursion is an idiomatic way of doing things in Scala. Recursive functions need an
-// explicit return type, the compile can't infer it. Here it's Unit.
+// A do while loop
+do {
+ println("x is still less then 10");
+ x += 1
+} while (x < 10)
+
+// Tail recursion is an idiomatic way of doing recurring things in Scala. Recursive functions need an
+// explicit return type, the compiler can't infer it. Here it's Unit.
def showNumbersInRange(a:Int, b:Int):Unit = { print(a); if (a < b) showNumbersInRange(a+1, b) }
@@ -175,7 +247,7 @@ 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("nope")
+if (x == 11) println ("yeah") else println("nay")
println(if (x == 10) "yeah" else "nope")
val text = if (x == 10) "yeah" else "nope"
@@ -183,8 +255,21 @@ val text = if (x == 10) "yeah" else "nope"
var i = 0
while (i < 10) { println("i " + i); i+=1 }
+
+
// Object oriented features
+// Classname is Dog
+class Dog {
+ //A method called bark, returning a String
+ def bark: String = {
+ // the body of the method
+ "Woof, woof!"
+ }
+}
+
+// Classes can contain nearly any other construct, including other classes, functions, methods, objects, case classes, traits etc.
+
// Case classes
@@ -230,6 +315,12 @@ val email(user, domain) = "henry@zkpr.com"
// 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 // See scala.collection.immutable.StringOps
+
println("ABCDEF".length)
println("ABCDEF".substring(2, 6))
println("ABCDEF".replace("C", "3"))
@@ -250,8 +341,45 @@ val html = """<form id="daform">
</form>"""
+
+// Application structure and organization
+
+// Importing things
+import scala.collection.immutable.List
+
+// Import all "sub packages"
+import scala.collection.immutable._
+
+// Import multiple classes in one statement
+import scala.collection.immutable.{List, Map}
+
+// Rename an import using '=>'
+import scala.collection.immutable{ List => ImmutableList }
+
+// Import all classes, except some. The following excludes Map and Set:
+import scala.collection.immutable.{Map => _, Set => _, _}
+
+// Your programs entry point is defined in an scala file using an object, with a single method, main:
+object Application {
+ def main(args: Array[String]): Unit = {
+ // stuff goes here.
+ }
+}
+
+// Files can contain multiple classes and objects. Compile with scalac
+
+
+
+
// Input and output
+// To read a file line by line
+import scala.io.Source
+for(line <- Source.fromPath("myfile.txt").getLines())
+ println(line)
+
+// To write a file use Java's PrintWriter
+
```
@@ -263,4 +391,5 @@ val html = """<form id="daform">
[The scala documentation]
-Join the [Scala user group](https://groups.google.com/forum/#!forum/scala-user) \ No newline at end of file
+Join the [Scala user group](https://groups.google.com/forum/#!forum/scala-user)
+