Functional Software Architecture is architecture using functional programming. Not everything is different, but almost. Primarily:

• pervasive use of immutable data / value objects
• documented and controlled side effects
• higher-order abstractions, based on math
• combinator models

These four building blocks make for architecture that is more robust and more flexible than traditional OO architecture: fewer dependencies, better reuse, less complexity. Moreover, the abstraction facilities in FP are more powerful, affording better models that are closer to the domain, come with less technical overhead, and can dredge hidden domain knowledge to the surface. This all works well with the strategic patterns of DDD. The workshop gives an introduction with examples that you can follow along.