presto-main/src/main/java/io/prestosql/operator/PipelineContext.java/PipelineContext/acceptChildren
class PipelineContext:    public <C, R> List<R> acceptChildren(QueryContextVisitor<C, R> visitor, C context)
    {
        return drivers.stream()
                .map(driver -> driver.accept(visitor, context))
                .collect(toList());
    }