presto-parser/src/main/java/io/prestosql/sql/ExpressionFormatter.java/ExpressionFormatter/visitFrameBound
class ExpressionFormatter:        @Override
        public String visitFrameBound(FrameBound node, Void context)
        {
            switch (node.getType()) {
                case UNBOUNDED_PRECEDING:
                    return "UNBOUNDED PRECEDING";
                case PRECEDING:
                    return process(node.getValue().get(), context) + " PRECEDING";
                case CURRENT_ROW:
                    return "CURRENT ROW";
                case FOLLOWING:
                    return process(node.getValue().get(), context) + " FOLLOWING";
                case UNBOUNDED_FOLLOWING:
                    return "UNBOUNDED FOLLOWING";
            }
            throw new IllegalArgumentException("unhandled type: " + node.getType());
        }