!7

replace Var with ValuelessVar.
replace VarMap with Map<Var, O>.

abstract sclass Prop implements IStatement, IFieldsToList {}

static withToList record Did$HappenBefore$<A, B>(A event1, B event2) {}
static withToList record WhenDid$Happen(O event) extends Prop {}
static withToList record $HappensAtSecond$<A, B>(A event, B y) extends Prop {}
static withToList record $LessThan$<A, B>(A x, B y) extends Prop {}
static withToList record $BiggerThanOrEqualTo$<A, B>(A x, B y) extends Prop {}
static withToList record $AnyIntBiggerThan(O x) {}
static withToList record $is$(O a, O b) {}

sclass SimpleStatements {
  new L<Prop> statements;
  
  *() {}
  *(Prop... statements) { addAll(this.statements, statements); }
  
  O fulfill(IF1<Var, Prop> makeRecord) {
    new Var var;
    O result = null;
    Prop record = makeRecord.get(var);
    O[] a = record._fieldsToList();
    bigLoop: for (Prop prop : statements) {
      if (prop.getClass() != record.getClass()) continue;
      O[] b = prop._fieldsToList();
      if (b.length != a.length) fail("Bad argument length: " + record);
      for i over a:
        if (a[i] == var) {
          if (result != null && !eq(result, b[i]))
            continue bigLoop;
          result = b[i];
        } else
          if (!eq(a[i], b[i]))
            continue bigLoop;
            
      ret result;
    }
    null;
  }
}

static O answer(O p, SimpleStatements statements) {
  if p is WhenDid$Happen(O event) {
    ret statements.fulfill(var -> $HappensAtSecond$(event, var));
  }
  
  if p is Did$HappenBefore$(O event1, O event2) {
    Int time1 = optCast int(statements.fulfill(var -> $HappensAtSecond$(event1, var)));
    if (time1 == null) null;
  }
  
  null;
}

// full define $LessThan(int x, int y) = x < y;
static Bool checkProposition(Prop p) {
  if p is $LessThan$(int x, int y) { ret x < y; }
  if p is $BiggerThanOrEqualTo$(int x, int y) {
    ret not(checkProposition($LessThan$(x, y)));
  }
  null;
}

p-exp {
  SimpleStatements statements = new($HappensAtSecond$("stuff", 10));
  print(answer(print(WhenDid$Happen("stuff")), statements));
}