Thanks for drawing attention to this, I didn't know about it.

We should mention that the root directory name has to be the same as the name of the haskell package.

One correction: I think buildInputs = attrs.buildInputs // buildInputs; is supposed to be buildInputs = attrs.buildInputs ++ buildInputs; ?

To conceptually explain what this feature is for, would it be fair to recommend putting the examples you've written into a default.nix file, and likening that file roughly to what you'd use a stack.yaml for if you were using stack instead of nix to set up the build environment?

I don't understand the purpose of the buildInputs = [ zlib ]; part of the second example. I've been testing with libraries that depend on zlib (I'm building a project with scotty) and everything's been working fine without having to explicitly declare a zlib dependency anywhere in the nix setup.

Thanks @chris-martin for the notes and thanks for your patience on my reply.

1. I added the note that developPackage could be used as a simplified stack.yaml replacement.
2. Yes, I made the correction, that is right (++ instead of //).
3. I tried to explain the rationale for when you would need to override the derivation returned from developPackage to add buildInputs (when your package directly depends on those buildInputs, not just transitively).