✎ pp:scala-project [books]

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======= Scala @ PP =======

===== "Meta ideas" =====

Test-driven development

===== 1. Installation =====

===== 2. Syntax =====

2.1. Writing functions
2.2. Function evaluation (order of parameters in function call matters !)
     - using the ''=>'' to delay evaluation
2.3. Conditionals
     - '' def f(x : Int) = if (x >= 0) x else -x''
     - boolean expressions (''true'', ''false'', ''!b'', ''&&'', ''||'')
     - the "by value" definition using ''val''
     - example using def and val against a loop
    
     
Newton square root estimation

  * Blocks - expressions in Scala 
  * visibility of variables in blocks
  * local scoping (similar to let)
  * semicolons (optional)
  * tail recursion in Scala (only direct recursive calls are optimised @tailrec)
  * function types (''f : Int => Int'')
  * anonymous functions (''(x: Int, y: Int) => x + y'', '' x => x+x'')
  * currying (''def f(x: Int, y: Int)(z: Int):Int = x+y+z'')
  * higher-order functions (mapReduce implementation)

  * classes and **methods**
<code scala>
class Rational(x: Int, y: Int) { // creates a Type as well as a constructor for the new type
    def a = x
    def b = y
}

val r = new Rational(1,2)
</code>
  * ''toString'' and ''@override''
  * the ''require'' (a precondition on the caller of a function) (equivalent to) and ''assert'' (check the code is right)
  * **constructors**:
    * multiple constructors:
<code scala>
class ... {
  def this(x: Int) = this(x,1)
}
</code>

  * infix notation for functions
<code scala>
  r add s   /*same as*/ r.add(s)
  
  def < (param : Rational)  /* symbolic identifiers may contain operator symbols */
  
  def unary_- (...) /* to overload negation. Careful, white spaces can be interpreted as identifiers */
  
  /* the precedence of an operator is determined by its first character */
  /* precedence cannot be overridden by the programmer */
  
</code>

===== 3. Data representation ======

  * object definitions - singleton classes ''object Empty extends IntSet''
  * companion objects (one object per class)
  * annotation ''@main def birthday'' - can be called directly from compilation ''scala birthday ...''
  * ''println(s"Hello $name")''
  * **dynamic binding**
  * packages - organising sources - directories (not enforced by the fs)
<code scala>
import pack.Obj
</code>
  * traits (similar to interfaces in Java, but can have parameters, contain fields and defined functions)
  * object hierarchy in Scala
  * exceptions (similar to Scala)