Right, as you said it’s just code example - not prod version. You can simply use &Keyword.fetch!/2 instead. Also it’s easy for just 2 arguments - if you take look at my proposition with 4 arguments you will end up with way too much code.
Simple for you does not needs to mean simple for others and for sure same goes to my old code. For example your defcalculus macro takes more than 100 lines - that’s way too much (take a look at credo library). I’m not someone pro who decides what things are good or bad practices. I simply take a look at other libraries. When I’m writing code I think if I will understand it even after x years. Can you quickly say what this code is doing?
case left do
[{:when, ctx0, [e | es]}] -> [{:when, ctx0, [e, key | es]}]
[e] -> [e, key]
end
For sure it’s really easy example and most probably you would know it. Now here goes beginner and see: e and es which says exactly nothing. It’s just code style, sugar, but in matter especially when you are working in team.
defmacrop construct(state) do
quote location: :keep do
fn :new, @security_key ->
calculus(state: unquote(state), return: :ok)
end
|> eval(:new)
end
end
If I understand correctly this macro could be simply imported and there is no need to add it inside other macro. For sure one small macro in bigger macro is not a problem, but it’s not the only one you have in it. Even splitting it into few helper functions would make it much more readable.
Simply look at end of file:
end
end
end
end
end
it explains everything. 
