// applies a logic rule to a single fact
sclass LogicRuleApplier {
  // essential
  BasicLogicRule rule;
  O fact;
  
  // where does your output go
  swappable void addRewrittenRHS(O rhs, O trail) {
    print("Derived: " + rhs);
  }
  
  // optional
  new DeepZipTools tools;
  bool verbose, printNonMatches;

  run {
    // now we match the fact to our condition
    Map map = tools.deepZip(rule.lhs, fact);

    // Discard unless all keys are variables
    if (map != null && !all(keys(map), s -> tools.isVar(s))) map = null;
    
    if (map == null)
      ret with if (printNonMatches) print("Non-match: " + quote(rule.lhs) + " / " + quote(fact));

    // Now we have a proper mapping with the keys being variables!
    if (verbose) print("Match: " + quote(rule.lhs) + " / " + quote(fact));

    // Apply mapping to right hand side
    O rhs_replaced = tools.replaceVars(rule.rhs, map);
    if (verbose) print(+rhs_replaced);
    
    Map trail = litorderedmap(op := "applyLogicRuleToFact",
      +rule, +fact, +rhs_replaced);

    addRewrittenRHS(rhs_replaced, trail);
  }
}