evaluator is superclass of both interpreter and compiler. monad is interpreter only - as it essentially models continuations, you cannot know what a monadic com

evaluator is superclass of both interpreter and compiler. monad is interpreter only - as it essentially models continuations, you cannot know what a monadic computation will do without running it whereas compilers are static analysis transforms over a static AST data structure. monad : dynamic :: applicative : static. dynamic means control flow (continuations being the foundational control flow primitive that can express all others aka imperative programming); static means declarative, it’s a data structure (no control flow) which can be inspected and statically analysed and decomposed into components then reassembled, all without evaluating it. applicative permits zero cost abstractions where a declarative high level abstraction is compiled into a target implementation and baked such that the abstraction has no runtime cost. because it has no control flow, applicative also captures parallelism - a data transform can be massively parallelized because there is no control flow / dynamic runtime state to coordinate.