Rule execution

gistfile1.md

I want to build a system which uses rules. These rules will change hourly (i.e. "this rule is effective from 2pm to 6pm"). The rules must support arbitrarily complex logic on just 2-3 pre-defined variables and result in a boolean:

item.a > 10 && item.b == 0 || item.category == FOOTWEAR

These rules will be executed hundreds of times per second so I can't afford the overhead of plain old eval. I want to reload the current effective ruleset from the database hourly, precompile each rule's logic string and execute it via the quickest method possible. It might look something like this:

class Rule
  def applies?(item)
    precompiled_logic.execute(item, TOPLEVEL_BINDING)
  end
end

How can I do this? I'm using Ruby 2.1.

What about something simple like this:

RULES = {}

new_rule_str = "item.a > 10 && item.b == 0 || item.category == FOOTWEAR"
key = Digest::MD5.hexdigest(new_rule_str) # can be rule.id or something.

RULES[key] = eval("->(item) { #{new_rule_str} }")

# ...

RULES[key][item]

This precompiles the lambda on first run, then just calls it with the "item" parameter for every subsequent run.

I think I'm on the same page with @joeyAghion

Ah, great idea, guys. Thanks so much!