> types are basic building blocks Yes but they should also be compositional, one should build larger types from smaller types. This is how we scale to solving

> types are basic building blocks Yes but they should also be compositional, one should build larger types from smaller types. This is how we scale to solving difficult problems. > but currencies are a moving target and needs constant update to handle the quirks of the real world. This is a separate issue orthogonal to types. The problem of modelling the real world and what models might be more generally useful. No model is perfect, all have trade-offs. > In my book the string is a great way to store a country of origin As an implementation using a string sounds pragmatic, but that should not be its type! You should still create a currency type and parse into it. Then you won't accidentally pass an arbitrary string to a parameter that is supposed to be a currency.