Basic expression interpreter

interpreter.rb

class Interpreter
  attr_reader :user

  def initialize(user)
    @user = user
  end

  def evaluate(expression)
    return send(*expression.map { |arg| arg.is_a?(Array) ? evaluate(arg) : arg })
  end

  def and(*args)
    args.all?
  end

  def or(*args)
    args.any?
  end

  def older_than(age)
    user.age > age
  end

  def lives_in_state(state)
    user.state == state
  end

  def visible_until(timestamp)
    Time.now < Time.parse(timestamp)
  end
  
  # Add any arbitrary conditional methods here as needed to extend your
  # expression language. You'd need to add message as an attribute for this one.
  #
  # def unseen
  #   !SeenMessage.where(user_id: user.id, message_id: message.id).exists?
  # end
end

user = OpenStruct.new
user.name = 'bob'
user.age = 23
user.state = 'WA'

interpreter = Interpreter.new(user)
interpreter.evaluate(["and", ["older_than", 18], ["lives_in_state", "WA"]]) # => true
interpreter.evaluate(["and", ["older_than", 18], ["lives_in_state", "CA"]]) # => false
interpreter.evaluate(["or", ["older_than", 24], ["lives_in_state", "WA"]]) # => true
interpreter.evaluate(["or", ["older_than", 24], ["lives_in_state", "CA"]]) # => false

# Add a date after which the message will no longer show
interpreter.evaluate(["and", ["older_than", 18], ["lives_in_state", "WA"], ["visible_until", "2022-05-15"]])

# With just a few building blocks you can start evaluating some complex expressions
# Anyone > age 18 in washington or anyone in california
interpreter.evaluate(["or", ["and", ["older_than", 18], ["lives_in_state", "WA"]], ["lives_in_state", "CA"]])

# Each message would be given an expression
# messages_to_display = messages.select { |msg| interpreter.evaluate(msg.expression) }