Some of this is covered in "Functional Core, Imperative Shell", https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://

Some of this is covered in "Functional Core, Imperative Shell", https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/catalog/funct... Haskell programs tend to have this structure because pure functions aren't allowed to call impure functions.