--- language: scala filename: learn.scala author: George Petrov author_url: http://www.github.com/petrovg --- Scala - the scalable language ```c /* Set yourself up: 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: scala> This is the so called REPL. You can run commands in the REPL. Let do just that: */ println(10) // prints the integer 10 println("Boo!") // printlns the string Boo! // Evaluating a command gives you the type and value of the result 1 + 7 /* The above line results in: scala> 1 + 7 res29: Int = 8 This means the result of evaluating 1 + 7 is an object of type Int with a value of 8 1+7 will give you the same result */ // 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 = 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 result is the Int with a value 100 // 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 // Combinators s.map(sq) val sSquared = s. map(sq) sSquared.filter(_ < 10) sSquared.reduce (_+_) // 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. Research this further */ // Loops and iteration 1 to 5 val r = 1 to 5 r.foreach( println ) r foreach println // NB: Scala is quite lenien 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 ) var i = 0 while (i < 10) { println("i " + i); i+=1 } 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 // 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. def showNumbersInRange(a:Int, b:Int):Unit = { print(a); if (a < b) showNumbersInRange(a+1, b) } // Conditionals 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") println(if (x == 10) "yeah" else "nope") val text = if (x == 10) "yeah" else "nope" var i = 0 while (i < 10) { println("i " + i); i+=1 } // Object oriented features // Case classes case class Person(name:String, phoneNumber:String) Person("George", "1234") == Person("Kate", "1236") // Pattern matching val me = Person("George", "1234") me match { case Person(name, number) => "We matched someone : " + name + ", phone : " + number } me match { case Person(name, number) => "Match : " + name; case _ => "Hm..." } me match { case Person("George", number) => "Match"; case _ => "Hm..." } me match { case Person("Kate", number) => "Match"; case _ => "Hm..." } me match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" } val kate = Person("Kate", "1234") kate match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" } // Regular expressions val email = "(.*)@(.*)".r // The suffix .r invokes method r on String, which makes it a Regex val email(user, domain) = "henry@zkpr.com" "mrbean@pyahoo.com" match { case email(name, domain) => "I know your name, " + name } // Strings println("ABCDEF".length) println("ABCDEF".substring(2, 6)) println("ABCDEF".replace("C", "3")) val n = 45 println(s"We have $n apples") val a = Array(11, 9, 6) println(s"My second daughter is ${a(2-1)} years old") // Some characters need to be 'escaped', e.g. a double quote inside a string: val a = "They stood outside the \"Rose and Crown\"" // Triple double-quotes allow for strings to span multiple rows and contain funny characters val html = """

Press belo', Joe

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""" // Input and output ``` ## Further resources [Scala for the impatient](http://horstmann.com/scala/) [Twitter Scala school(http://twitter.github.io/scala_school/) [The scala documentation] Join the [Scala user group](https://groups.google.com/forum/#!forum/scala-user)