!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) {}

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;
}

replace SimpleStatements with MatchableRecords<Prop>.

p-exp {
  SimpleStatements statements = new(
    $HappensAtSecond$("stuff", 10),
    $HappensAtSecond$("more stuff", 20)
  );
  assertEqualsVerbose(10, answer(print(WhenDid$Happen("stuff")), statements));
  assertEqualsVerbose(20, answer(print(WhenDid$Happen("more stuff")), statements));
  assertEqualsVerbose(null, answer(print(WhenDid$Happen("something else")), statements));
}