presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitParameter
class AstBuilder:    @Override
    public Node visitParameter(SqlBaseParser.ParameterContext context)
    {
        io.prestosql.sql.tree.Parameter parameter = new io.prestosql.sql.tree.Parameter(getLocation(context), parameterPosition);
        parameterPosition++;
        return parameter;
    }