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A huge re-organization of the Scala file
This commit is contained in:
Geoff Liu
parent
459967e446
commit
57c9f70417
@ -4,6 +4,7 @@ filename: learnscala.scala
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contributors:
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- ["George Petrov", "http://github.com/petrovg"]
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- ["Dominic Bou-Samra", "http://dbousamra.github.com"]
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- ["Geoff Liu", "http://geoffliu.me"]
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filename: learn.scala
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---
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@ -20,16 +21,16 @@ Scala - the scalable language
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scala>
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This is the so called REPL. You can run commands in the REPL. Let's do just
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that:
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This is the so called REPL (Read-Eval-Print Loop). You may type any valid
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Scala expression into it, and the result will be printed. We will explain what
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Scala files look like further into this tutorial, but for now, let's start
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with some basics.
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*/
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println(10) // prints the integer 10
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println("Boo!") // printlns the string Boo!
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// Some basics
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#################################################
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## 1. Basics
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#################################################
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// Printing, and forcing a new line on the next print
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println("Hello world!")
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@ -37,15 +38,15 @@ println("Hello world!")
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print("Hello world")
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// Declaring values is done using either var or val
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// val declarations are immutable, whereas var's are mutable. Immutability is
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// val declarations are immutable, whereas var's are mutable. Immutability is
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// a good thing.
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val x = 10 // x is now 10
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x = 20 // error: reassignment to val
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var x = 10
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var x = 10
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x = 20 // x is now 20
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// Single line comments start with two forward slashes
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/*
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/*
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Multi line comments look like this.
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*/
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@ -82,262 +83,6 @@ true == false // false
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*/
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// Everything is an object, including a function. Type these in the REPL:
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7 // results in res30: Int = 7 (res30 is just a generated var name for the result)
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// The next line gives you a function that takes an Int and returns it squared
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(x:Int) => x * x
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// You can assign this function to an identifier, like this:
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val sq = (x:Int) => x * x
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/* The above says this
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sq: Int => Int = <function1>
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Which means that this time we gave an explicit name to the value - sq is a
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function that take an Int and returns Int.
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sq can be executed as follows:
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*/
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sq(10) // Gives you this: res33: Int = 100.
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// The colon explicitly defines the type of a value, in this case a function
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// taking an Int and returning an Int.
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val add10: Int => Int = _ + 10
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// Scala allows methods and functions to return, or take as parameters, other
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// functions or methods.
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List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element
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// Anonymous functions can be used instead of named functions:
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List(1, 2, 3) map (x => x + 10)
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// And the underscore symbol, can be used if there is just one argument to the
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// anonymous function. It gets bound as the variable
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List(1, 2, 3) map (_ + 10)
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// If the anonymous block AND the function you are applying both take one
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// argument, you can even omit the underscore
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List("Dom", "Bob", "Natalia") foreach println
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// Data structures
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val a = Array(1, 2, 3, 5, 8, 13)
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a(0)
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a(3)
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a(21) // Throws an exception
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val m = Map("fork" -> "tenedor", "spoon" -> "cuchara", "knife" -> "cuchillo")
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m("fork")
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m("spoon")
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m("bottle") // Throws an exception
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val safeM = m.withDefaultValue("no lo se")
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safeM("bottle")
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val s = Set(1, 3, 7)
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s(0)
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s(1)
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/* Look up the documentation of map here -
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* http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map
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* and make sure you can read it
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*/
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// Tuples
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(1, 2)
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(4, 3, 2)
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(1, 2, "three")
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(a, 2, "three")
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// Why have this?
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val divideInts = (x:Int, y:Int) => (x / y, x % y)
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divideInts(10,3) // The function divideInts gives you the result and the remainder
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// To access the elements of a tuple, use _._n where n is the 1-based index of
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// the element
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val d = divideInts(10,3)
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d._1
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d._2
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// Combinators
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s.map(sq)
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val sSquared = s. map(sq)
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sSquared.filter(_ < 10)
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sSquared.reduce (_+_)
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// The filter function takes a predicate (a function from A -> Boolean) and
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// selects all elements which satisfy the predicate
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List(1, 2, 3) filter (_ > 2) // List(3)
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List(
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Person(name = "Dom", age = 23),
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Person(name = "Bob", age = 30)
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).filter(_.age > 25) // List(Person("Bob", 30))
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// Scala a foreach method defined on certain collections that takes a type
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// returning Unit (a void method)
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aListOfNumbers foreach (x => println(x))
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aListOfNumbers foreach println
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// For comprehensions
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for { n <- s } yield sq(n)
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val nSquared2 = for { n <- s } yield sq(n)
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for { n <- nSquared2 if n < 10 } yield n
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for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
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/* NB Those were not for loops. The semantics of a for loop is 'repeat', whereas
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a for-comprehension defines a relationship between two sets of data. */
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// Loops and iteration
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1 to 5
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val r = 1 to 5
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r.foreach( println )
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r foreach println
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// NB: Scala is quite lenient when it comes to dots and brackets - study the
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// rules separately. This helps write DSLs and APIs that read like English
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(5 to 1 by -1) foreach ( println )
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// A while loops
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var i = 0
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while (i < 10) { println("i " + i); i+=1 }
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while (i < 10) { println("i " + i); i+=1 } // Yes, again. What happened? Why?
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i // Show the value of i. Note that while is a loop in the classical sense -
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// it executes sequentially while changing the loop variable. while is very
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// fast, faster that Java // loops, but using the combinators and
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// comprehensions above is easier to understand and parallelize
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// A do while loop
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do {
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println("x is still less than 10");
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x += 1
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} while (x < 10)
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// Tail recursion is an idiomatic way of doing recurring things in Scala.
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// Recursive functions need an explicit return type, the compiler can't infer it.
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// Here it's Unit.
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def showNumbersInRange(a:Int, b:Int):Unit = {
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print(a)
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if (a < b)
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showNumbersInRange(a + 1, b)
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}
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// Conditionals
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val x = 10
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if (x == 1) println("yeah")
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if (x == 10) println("yeah")
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if (x == 11) println("yeah")
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if (x == 11) println ("yeah") else println("nay")
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println(if (x == 10) "yeah" else "nope")
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val text = if (x == 10) "yeah" else "nope"
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var i = 0
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while (i < 10) { println("i " + i); i+=1 }
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// Object oriented features
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// Classname is Dog
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class Dog {
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//A method called bark, returning a String
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def bark: String = {
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// the body of the method
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"Woof, woof!"
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}
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}
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// Classes can contain nearly any other construct, including other classes,
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// functions, methods, objects, case classes, traits etc.
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// Case classes
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case class Person(name:String, phoneNumber:String)
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Person("George", "1234") == Person("Kate", "1236")
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// Pattern matching
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val me = Person("George", "1234")
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me match { case Person(name, number) => {
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"We matched someone : " + name + ", phone : " + number }}
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me match { case Person(name, number) => "Match : " + name; case _ => "Hm..." }
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me match { case Person("George", number) => "Match"; case _ => "Hm..." }
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me match { case Person("Kate", number) => "Match"; case _ => "Hm..." }
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me match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
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val kate = Person("Kate", "1234")
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kate match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
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// Regular expressions
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val email = "(.*)@(.*)".r // Invoking r on String makes it a Regex
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val serialKey = """(\d{5})-(\d{5})-(\d{5})-(\d{5})""".r // Using verbatim (multiline) syntax
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val matcher = (value: String) => {
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println(value match {
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case email(name, domain) => s"It was an email: $name"
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case serialKey(p1, p2, p3, p4) => s"Serial key: $p1, $p2, $p3, $p4"
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case _ => s"No match on '$value'" // default if no match found
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})
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}
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matcher("mrbean@pyahoo.com") // => "It was an email: mrbean"
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matcher("nope..") // => "No match on 'nope..'"
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matcher("52917") // => "No match on '52917'"
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matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917"
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// Strings
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"Scala strings are surrounded by double quotes" //
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@ -379,8 +124,291 @@ val html = """<form id="daform">
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</form>"""
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#################################################
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## 2. Functions
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#################################################
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// Application structure and organization
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// The next line gives you a function that takes an Int and returns it squared
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(x:Int) => x * x
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// You can assign this function to an identifier, like this:
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val sq = (x:Int) => x * x
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/* The above says this
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sq: Int => Int = <function1>
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Which means that this time we gave an explicit name to the value - sq is a
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function that take an Int and returns Int.
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sq can be executed as follows:
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*/
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sq(10) // Gives you this: res33: Int = 100.
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// The colon explicitly defines the type of a value, in this case a function
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// taking an Int and returning an Int.
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val add10: Int => Int = _ + 10
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#################################################
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## 3. Flow Control
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#################################################
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1 to 5
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val r = 1 to 5
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r.foreach( println )
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r foreach println
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// NB: Scala is quite lenient when it comes to dots and brackets - study the
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// rules separately. This helps write DSLs and APIs that read like English
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(5 to 1 by -1) foreach ( println )
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// A while loops
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var i = 0
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while (i < 10) { println("i " + i); i+=1 }
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while (i < 10) { println("i " + i); i+=1 } // Yes, again. What happened? Why?
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i // Show the value of i. Note that while is a loop in the classical sense -
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// it executes sequentially while changing the loop variable. while is very
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// fast, faster that Java // loops, but using the combinators and
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// comprehensions above is easier to understand and parallelize
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// A do while loop
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do {
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println("x is still less than 10");
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x += 1
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} while (x < 10)
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// Tail recursion is an idiomatic way of doing recurring things in Scala.
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// Recursive functions need an explicit return type, the compiler can't infer it.
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// Here it's Unit.
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def showNumbersInRange(a:Int, b:Int):Unit = {
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print(a)
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if (a < b)
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showNumbersInRange(a + 1, b)
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}
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// Conditionals
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val x = 10
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if (x == 1) println("yeah")
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if (x == 10) println("yeah")
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if (x == 11) println("yeah")
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if (x == 11) println ("yeah") else println("nay")
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println(if (x == 10) "yeah" else "nope")
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val text = if (x == 10) "yeah" else "nope"
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var i = 0
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while (i < 10) { println("i " + i); i+=1 }
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#################################################
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## 4. Data Structures
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#################################################
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val a = Array(1, 2, 3, 5, 8, 13)
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a(0)
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a(3)
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a(21) // Throws an exception
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val m = Map("fork" -> "tenedor", "spoon" -> "cuchara", "knife" -> "cuchillo")
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m("fork")
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m("spoon")
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m("bottle") // Throws an exception
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val safeM = m.withDefaultValue("no lo se")
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safeM("bottle")
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val s = Set(1, 3, 7)
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s(0)
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s(1)
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/* Look up the documentation of map here -
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* http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map
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* and make sure you can read it
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*/
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// Tuples
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(1, 2)
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(4, 3, 2)
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(1, 2, "three")
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(a, 2, "three")
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|
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// Why have this?
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val divideInts = (x:Int, y:Int) => (x / y, x % y)
|
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|
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divideInts(10,3) // The function divideInts gives you the result and the remainder
|
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|
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// To access the elements of a tuple, use _._n where n is the 1-based index of
|
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// the element
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val d = divideInts(10,3)
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d._1
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d._2
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#################################################
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## 5. Object Oriented Programming
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#################################################
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/*
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Aside: Everything we've done so far in this tutorial has been simple
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expressions (values, functions, etc). These expressions are fine to type into
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the command-line interpreter for quick tests, but they cannot exist by
|
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themselves in a Scala file. For example, you cannot have just "val x = 5" in
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a Scala file. Instead, the only top-level constructs allowed in Scala are:
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|
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- objects
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- classes
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- case classes
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- traits
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And now we will explain what these are.
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*/
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|
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class Dog {
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//A method called bark, returning a String
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def bark: String = {
|
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// the body of the method
|
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"Woof, woof!"
|
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}
|
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}
|
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|
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// Classes can contain nearly any other construct, including other classes,
|
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// functions, methods, objects, case classes, traits etc.
|
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|
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// Case classes
|
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|
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case class Person(name:String, phoneNumber:String)
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Person("George", "1234") == Person("Kate", "1236")
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// Objects and traits coming soon!
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#################################################
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## 6. Pattern Matching
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#################################################
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val me = Person("George", "1234")
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me match { case Person(name, number) => {
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"We matched someone : " + name + ", phone : " + number }}
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me match { case Person(name, number) => "Match : " + name; case _ => "Hm..." }
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me match { case Person("George", number) => "Match"; case _ => "Hm..." }
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me match { case Person("Kate", number) => "Match"; case _ => "Hm..." }
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me match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
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val kate = Person("Kate", "1234")
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kate match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
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// Regular expressions
|
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val email = "(.*)@(.*)".r // Invoking r on String makes it a Regex
|
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val serialKey = """(\d{5})-(\d{5})-(\d{5})-(\d{5})""".r // Using verbatim (multiline) syntax
|
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|
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val matcher = (value: String) => {
|
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println(value match {
|
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case email(name, domain) => s"It was an email: $name"
|
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case serialKey(p1, p2, p3, p4) => s"Serial key: $p1, $p2, $p3, $p4"
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case _ => s"No match on '$value'" // default if no match found
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})
|
||||
}
|
||||
|
||||
matcher("mrbean@pyahoo.com") // => "It was an email: mrbean"
|
||||
matcher("nope..") // => "No match on 'nope..'"
|
||||
matcher("52917") // => "No match on '52917'"
|
||||
matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917"
|
||||
|
||||
|
||||
#################################################
|
||||
## 7. Functional Programming
|
||||
#################################################
|
||||
|
||||
// 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
|
||||
|
||||
|
||||
// Combinators
|
||||
|
||||
s.map(sq)
|
||||
|
||||
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!
|
||||
|
||||
|
||||
#################################################
|
||||
## 9. Misc
|
||||
#################################################
|
||||
|
||||
// Importing things
|
||||
import scala.collection.immutable.List
|
||||
|
||||
Loading…
Reference in New Issue
Block a user