Call-by-value - Call-by-name

  • CBV: arguments are evaluated before substituting the function call with the function’s RHS and the parameters with values
  • CBN: substituting function and parameters then evaluating parameters
  • By default, parameters are CBV. Use =>, e.g. (x: Int, y: => Int), for CBN
  • def: by-name - val: by-value

Tail recursion:

  • When a recursive function calls itself in the same form, so the call stack can be reused.
  • In other words, there’s no need to store immediate values, arguments for the next call can be put into the existing stack frame.


for expression <=> flatMap, withFilter, and map


To define a prefix operator, write: def unary_- : <type> = {}, the space before : is required to not make the colon a part of the identifier. Only 4 operators can be used: + - ! ~

To refer to a method foo from a function foo inside another method, write like this

trait Bar {
  self =>

  def foo: T
  def waz: U = {
    def foo = // or like Java:

Only the primary constructor of a class can call the superclass constructor.
Every auxiliary constructor must invoke another constructor as its first action.

Traits further to the right take effect first: the method at the rightest is called first; if it calls super, it invokes the method in the trait to its left.