diff options
| -rw-r--r-- | scala.html.markdown | 86 |
1 files changed, 53 insertions, 33 deletions
diff --git a/scala.html.markdown b/scala.html.markdown index 8e00f135..687914ef 100644 --- a/scala.html.markdown +++ b/scala.html.markdown @@ -8,9 +8,7 @@ filename: learn.scala Scala - the scalable language -```c - - +```scala /* Set yourself up: @@ -21,7 +19,8 @@ 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. You can run commands in the REPL. Let's do just + that: */ println(10) // prints the integer 10 @@ -37,7 +36,8 @@ println("Hello world!") 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 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 @@ -74,7 +74,8 @@ true == false // false 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 + 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 */ @@ -94,14 +95,16 @@ val sq = (x:Int) => x * x 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. + 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 +sq(10) // Gives you this: res33: Int = 100. -// Scala allows methods and functions to return, or take as parameters, other functions or methods. +// 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 @@ -109,10 +112,12 @@ 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 +// 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 +// 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 @@ -136,7 +141,8 @@ 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 +/* 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 */ @@ -156,7 +162,8 @@ 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 +// 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 @@ -175,7 +182,8 @@ sSquared.filter(_ < 10) sSquared.reduce (_+_) -// The filter function takes a predicate (a function from A -> Boolean) and selects all elements which satisfy the predicate +// 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), @@ -183,7 +191,8 @@ List( ).filter(_.age > 25) // List(Person("Bob", 30)) -// Scala a foreach method defined on certain collections that takes a type returning Unit (a void method) +// 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 @@ -200,8 +209,8 @@ 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 */ +/* 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. */ @@ -212,8 +221,8 @@ 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 +// 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 ) @@ -223,20 +232,25 @@ 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 +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 // A do while loop -do { +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) } +// 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) +} @@ -268,7 +282,8 @@ class Dog { } } -// Classes can contain nearly any other construct, including other classes, functions, methods, objects, case classes, traits etc. +// Classes can contain nearly any other construct, including other classes, +// functions, methods, objects, case classes, traits etc. @@ -285,7 +300,8 @@ Person("George", "1234") == Person("Kate", "1236") val me = Person("George", "1234") -me match { case Person(name, number) => "We matched someone : " + name + ", phone : " + number } +me match { case Person(name, number) => { + "We matched someone : " + name + ", phone : " + number }} me match { case Person(name, number) => "Match : " + name; case _ => "Hm..." } @@ -303,7 +319,7 @@ 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 = "(.*)@(.*)".r // Invoking r on String makes it a Regex val email(user, domain) = "henry@zkpr.com" @@ -319,7 +335,9 @@ val email(user, domain) = "henry@zkpr.com" '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 +"They also have some extra Scala methods.".reverse + +// Seealso: scala.collection.immutable.StringOps println("ABCDEF".length) println("ABCDEF".substring(2, 6)) @@ -334,7 +352,8 @@ 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 +// Triple double-quotes let strings span multiple rows and contain quotes + val html = """<form id="daform"> <p>Press belo', Joe</p> | <input type="submit"> @@ -359,7 +378,8 @@ 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: +// 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. |