Mentioned elsewhere but that is largely the heart of Functional Core, Imperative Shell: https://www.destroyallsoftware.com/screencasts/catalog/functional-core-i

Mentioned elsewhere but that is largely the heart of Functional Core, Imperative Shell: https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/catalog/funct... (And I am sure a bunch of other similar but differently-named concepts)