promql/engine.go
func (ng *Engine) NewInstantQuery(q storage.Queryable, qs string, ts time.Time) (Query, error) {
	expr, err := ParseExpr(qs)
	if err != nil {
		return nil, err
	}
	qry := ng.newQuery(q, expr, ts, ts, 0)
	qry.q = qs

	return qry, nil
}
func (ng *Engine) NewInstantQuery(q storage.Queryable, qs string, ts time.Time) (Query, error) {
	expr, err := ParseExpr(qs)
	if err != nil {
		return nil, err
	}
	qry := ng.newQuery(q, expr, ts, ts, 0)
	qry.q = qs

	return qry, nil
}
// NewInstantQuery returns an evaluation query for the given expression at the given time.