sinterface ISearchVar {
  bool set(O o);
  O get();
}

sclass MatchVar<A extends Concept> implements IRef<A>, ISearchVar {
  A value;
  Class<A> type;
  
  public A get() { ret value; }
  
  public S toString() { ret str(value); }
  
  bool canHold(O o) { ret type == null || isInstance(type, o); }
  
  public bool set(O o) { if (canHold(o)) { value = (A) o; true; } else false; }
}

sclass Subsearch {
  Class c;
  O[] params;

  *(Class *c, O[] params) {
    this.params = expandParams(c, params);
  }
}

static Subsearch some(Class<? extends Concept> c, O... params) {
  ret new Subsearch(c, params);
}

static <A extends Concept> A searchConcept(MatchVar<A> var, O... params) {
  assertNotNull(var.type); // must be typed to use in place of class
  ret var.value = searchConcept(var.type, params);
}

static <A extends Concept> A searchConcept(Class<A> c, O... params) {
  params = expandParams(c, params);
  // First, go through all the concepts of the primary type.
  for (A concept : list(c))
    if (searchConcept_checkParams(concept, params))
      ret concept; // Success!
  null;
}

static <A extends Concept> L<A> searchConcept_all(Class<A> c, O... params) {
  params = expandParams(c, params);
  new L<A> l;
  // First, go through all the concepts of the primary type.
  for (A concept : list(c))
    if (searchConcept_checkParams(concept, params))
      l.add(concept); // Success!
  ret l;
}

static bool searchConcept_checkParams(Concept c, O... params) {
  for (int i = 0; i+1 < l(params); i += 2) {
    S field = cast params[i];
    O val = derefRef(params[i+1]);
    O actual = cget(c, field);
    if (val instanceof Subsearch) {
      Subsearch s = cast val;
      if (!isInstance(s.c, actual)) false; // wrong type
      if (!searchConcept_checkParams((Concept) actual, s.params)) false; // bad params
    } else if (val instanceof ISearchVar) {
      ISearchVar v = cast val;
      if (!v.set(actual)) false;
    } else
      if (neq(actual, val)) false;
  }
  true; // all params match
}

sbool actually(Class c, O... params) {
  ret searchConcept(Actually, some(c, params)) != null;
}

/*sbool actually(MatchVar var, O... params) {
  ret searchConcept(Actually, some(var, params)) != null;
}*/

/*static L<Concept> listActually(MatchVar var, O... params) {
  ret map(func(Actually a) { a.what.get() }, searchConcept_all(Actually, some(var, params)));
}*/

static <A extends Concept> L<A> listActually(Class<A> c, O... params) {
  ret map(func(Actually a) { a.what.get() }, searchConcept_all(Actually, some(c, params)));
}

static <A extends Concept> MatchVar<A> typedVar(Class<A> c) {
  new MatchVar<A> var;
  var.type = c;
  ret var;
}

Began life as a copy of #1005324