Scala @ PP

Test-driven development

2.1. Writing functions 2.2. Function evaluation (order of parameters in function call matters !)

1. using the ⇒ to delay evaluation

2.3. Conditionals

1. def f(x : Int) = if (x >= 0) x else -x
2. boolean expressions (true, false, !b, &&, ||)
3. the “by value” definition using val
4. 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

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)

• 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:

class ... {
  def this(x: Int) = this(x,1)
}

• infix notation for functions

  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 */
 

• 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 ”)
• dynamic binding
• packages - organising sources - directories (not enforced by the fs)

import pack.Obj

• traits (similar to interfaces in Java, but can have parameters, contain fields and defined functions)
• object hierarchy in Scala
• exceptions (similar to Scala)