ClickHouse/dbms/src/Parsers/IParser.h
2017-07-13 08:59:01 +03:00

95 lines
2.3 KiB
C++

#pragma once
#include <set>
#include <memory>
#include <Core/Defines.h>
#include <Core/Types.h>
#include <Parsers/IAST.h>
#include <Parsers/TokenIterator.h>
namespace DB
{
/** Collects variants, how parser could proceed further at rightmost position.
*/
struct Expected
{
const char * max_parsed_pos = nullptr;
std::set<const char *> variants;
/// 'description' should be statically allocated string.
void add(const char * current_pos, const char * description)
{
if (!max_parsed_pos || current_pos > max_parsed_pos)
{
variants.clear();
max_parsed_pos = current_pos;
}
if (!max_parsed_pos || current_pos >= max_parsed_pos)
variants.insert(description);
}
void add(TokenIterator it, const char * description)
{
add(it->begin, description);
}
};
/** Interface for parser classes
*/
class IParser
{
public:
using Pos = TokenIterator;
/** Get the text of this parser parses. */
virtual const char * getName() const = 0;
/** Parse piece of text from position `pos`, but not beyond end of line (`end` - position after end of line),
* move pointer `pos` to the maximum position to which it was possible to parse,
* in case of success return `true` and the result in `node` if it is needed, otherwise false,
* in `expected` write what was expected in the maximum position,
* to which it was possible to parse if parsing was unsuccessful,
* or what this parser parse if parsing was successful.
* The string to which the [begin, end) range is included may be not 0-terminated.
*/
virtual bool parse(Pos & pos, ASTPtr & node, Expected & expected) = 0;
bool ignore(Pos & pos, Expected & expected)
{
ASTPtr ignore_node;
return parse(pos, ignore_node, expected);
}
bool ignore(Pos & pos)
{
Expected expected;
return ignore(pos, expected);
}
/** The same, but do not move the position and do not write the result to node.
*/
bool check(Pos & pos, Expected & expected)
{
Pos begin = pos;
ASTPtr node;
if (!parse(pos, node, expected))
{
pos = begin;
return false;
}
else
return true;
}
virtual ~IParser() {}
};
using ParserPtr = std::unique_ptr<IParser>;
}