> If you can reason about f and g that doesn’t mean that you can tell anything useful about f o g What? The ability to reason about f o g (for various definiti

> If you can reason about f and g that doesn’t mean that you can tell anything useful about f o g What? The ability to reason about f o g (for various definitions of o) is the promise of Haskell and one of its entire ecosystem's foundational principles. Local reasoning is absolutely possible.