Really, quite a few of these hold outside of Haskell as well. * "reduce the interactions between components by relying on pure interfaces" * use purely functi

Really, quite a few of these hold outside of Haskell as well. * "reduce the interactions between components by relying on pure interfaces" * use purely functional data structures to model key parts of the world you're talking to. Model-driven design with easy to verify logic * Avoid partial functions Pure interfaces require you to declare all context, and it's arguably all the context implicit in typical OO software that kills reusability. As Joe Armstrong put it, "...the problem with object-oriented languages is they've got all this implicit environment that they carry around with them. You wanted a banana but what you got was a gorilla holding the banana and the entire jungle." * use types to encode the design into a machine checkable form * picking a good data type (like a zipper) will make hundreds of unit tests meaningless -- improving productivity. The point of static typing is to structure code in a way that more assumptions can be expressed and automatically checked. A well-chosen data structure brings with it all of its expected behavior. * ensure components have 'axiomatic' interfaces -- reduce complexity by avoiding redundancy * if at all possible ensure your core algorithms and logic are referentially transparent -- this will dramatically simplify maintainanace and QA effort "Declarative programming clears the mind." - Sterling & Shapiro, _The Art of Prolog_