!7

sclass Improver<A, B> {
  O guesser; // func(A) -> B
  new HashMap<A, B> examples;
  new HashSet<A> errorExamples;
  new O error;
  
  B get(A a) {
    if (errorExamples.contains(a)) fail();
    if (examples.containsKey(a))
      ret examples.get(a);
    try {
      B b = (B) callF(guesser, a);
      examples.put(a, b);
      ret b;
    } catch e {
      errorExamples.add(a);
      throw rethrow(e);
    }
  }
  
  void addExample(A a, B b) {
    examples.put(a, b);
    errorExamples.remove(a);
  }
}

p {
  new Improver i;
  print("hello => " + i.get("hello"));
  i.addExample("hello", "world");
  print("hello => " + i.get("hello"));
}