I'm not sure I'm following you regarding the difficulty of encoding business logic into your code in Erlang.

Erlang's function-head matching system is extremely close to being a Prolog-style logic programming system when used a certain way.

I've found it extremely easy to take what would normally be a big weird database of rules and values and instead precompile every possible route through the system into a bunch of generated function-head matched function calls + guard clauses. It makes assuring that given inputs will definitely produce correct outputs very easy, and makes processing the rules extremely fast.