Exactly! Beat me to it. This is a constant source of bugs in software: developer making a "reasonable" judgement that gets crushed by reality. The core idea i

Exactly! Beat me to it. This is a constant source of bugs in software: developer making a "reasonable" judgement that gets crushed by reality. The core idea is true, though. Enumeration types, set operations and pattern matching are must-have features in any PL.