Chapter 4 - Datatypes
Added degree datatype
Disjoint sum/union
Scala example of problems of not overriding hashCode
Chapter 4 - making change
Scala port of Erik Meijer's lazy evaluation and side-effects slide
More from Chapter 3 - making change
Scala port of Erik Meijer's Variable Instantiation slide
Erik Meijer's lazy evaluation with side effects side in Haskell
Chapter 4 tautology checker
a little Haskell example