It's by Gary Bernhardt: https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/c

It's by Gary Bernhardt: https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/catalog/funct... He also did another talk expanding the concept called Boundaries: https://www.destroyallsoftware.com/talks/boundaries https://www.destroyallsoftware.com/talks/boundaries