presto-main/src/main/java/io/prestosql/spi/expression/PartialTranslator.java/PartialTranslator/visitExpression
class PartialTranslator:        @Override
        public Void visitExpression(Expression node, Void context)
        {
            Optional<ConnectorExpression> result = translator.process(node);

            if (result.isPresent()) {
                translatedSubExpressions.put(NodeRef.of(node), result.get());
            }
            else {
                node.getChildren().forEach(this::process);
            }

            return null;
        }