Can you write your own home-grown rules engine in Ruby: yes.
Can you use off-the-shelf gems: yes. Here's a few I poked around in my previous explorations into Ruby Rules Engines:
* durable rules - https://github.com/jruizgit/rules?tab=readme-ov-file#ruby
* wongi - https://github.com/ulfurinn/wongi-engine
* rules - https://github.com/azach/rules
* ruleby - https://github.com/Ruleby/ruleby
- bonus: video of original ruleby author explaining rules engines: https://www.youtube.com/watch?v=qMh2RDL6aBM
Can you write your own home-grown rules engine in Ruby: yes.
Can you use off-the-shelf gems: yes. Here's a few I poked around in my previous explorations into Ruby Rules Engines:
* durable rules - https://github.com/jruizgit/rules?tab=readme-ov-file#ruby
* wongi - https://github.com/ulfurinn/wongi-engine
* rules - https://github.com/azach/rules
* ruleby - https://github.com/Ruleby/ruleby
edit: It's also possible to write your own Ruby gem in C so that you can pass the handling of the RHS of your rules to a Ruby script.