// 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);

  }

}