> In Haskell, I come up with a coherent skeleton without having to implement mundane details, hit a wall in the design space because of some case I didn't think of, come up with a better idea and then go back to the code and refactor with confidence. The type system always guarantees that my prototype is coherent as a whole. And I can do that dozens of times.
Could you go into a bit of detail about this approach? Do you mock functions out and just specify type definitions, and fill in functionality as you go?
Note that src/Hotep.hs exports a bunch of undefined functions. I've been able to verify that these types all make sense even without implementing a thing. As time goes on I may learn that the implementation drives the types somewhere else and then the compiler will make refactoring easy.
However, already I've gone through about 5 iterations of this design which drove me to debug some structural questions about the whole affair and also dive deep into Erlang documentation to determine how they solved problems. These explorations and their results are encoded into the types.
At this point I'm beginning to consider implementation and I can keep filling out just partial implementations against these types. I'll probably make 2 or 3 toy implementations to test out the ideas again with more strength before moving on the final ones. The whole time the types will be guiding that development and helping it move quickly.
Key to this whole affair is the need to describe types utterly before a completely successful library is made... and also the ability to defer the burden of providing type-checking code for as long as desirable. Haskell supports this wonderfully—even more wonderfully with things like Typed Holes and Deferred Type Errors which enable a really great interactive experience I haven't yet needed to employ.
Could you go into a bit of detail about this approach? Do you mock functions out and just specify type definitions, and fill in functionality as you go?