I'm always surprised that this style of architecture isn't discussed in terms of functional purity [1]. To me, a hexagonal architecture essentially means creat

I'm always surprised that this style of architecture isn't discussed in terms of functional purity [1]. To me, a hexagonal architecture essentially means creating an abstraction at the point between pure and impure functions. The realization of this approach essentially means the core of your application should be entirely pure and as large as possible. And your impure adapters, at the application boundary, (e.g. a rest api, db client, file system, system clock, etc.) should be as small as possible and impure. Doing this well essentially allows you to get the best of both worlds - highly coupled code (i.e.your pure functionality) and highly decoupled code (i.e. your pure-to-impure functionality). Another good reason for leveraging "functional design" as an argument is that many of those skeptical of architectural patterns are ironically heavily onboard the "functional design" bandwagon. So it is a strong argument in a political sense also. [1] https://en.wikipedia.org/wiki/Pure_function https://en.wikipedia.org/wiki/Pure_function