这是一个有趣的练习，我
最终编写了一个可行的
on_success[1]演示来注释AST节点。
假设我们想要一个类似这样的AST：
namespace ast
{
struct LocationInfo {
unsigned line, column, length;
};
struct Identifier : LocationInfo {
std::string name;
};
struct VarAssignment : LocationInfo {
Identifier id;
int value;
};
struct SourceCode : LocationInfo {
Identifier function;
std::vector<VarAssignment> assignments;
};
}
我知道，“位置信息”对于SourceCode节点来说可能有点过头，但你懂的...总之，为了使其易于为这些节点分配属性而无需使用语义动作或大量特别制作的构造函数：
BOOST_FUSION_ADAPT_STRUCT(ast::Identifier, (std::string, name))
BOOST_FUSION_ADAPT_STRUCT(ast::VarAssignment, (ast::Identifier, id)(int, value))
BOOST_FUSION_ADAPT_STRUCT(ast::SourceCode, (ast::Identifier, function)(std::vector<ast::VarAssignment>, assignments))
好的，现在我们可以声明规则来公开这些属性：
qi::rule<Iterator, ast::SourceCode(), Skipper> SourceCode;
qi::rule<Iterator, ast::VarAssignment(), Skipper> VarAssignment;
qi::rule<Iterator, ast::Identifier()> Identifier;
// no skipper, no attributes:
qi::rule<Iterator> KeywordFunction, KeywordVar, SemiColon;
我们基本上不修改语法: 属性传播“只是自动的”。
[2]
KeywordFunction = lit("function");
KeywordVar = lit("var");
SemiColon = lit(';');
Identifier = as_string [ alpha >> *(alnum | char_("_")) ];
VarAssignment = KeywordVar >> Identifier >> '=' >> int_ >> SemiColon;
SourceCode = KeywordFunction >> Identifier >> '{' >> *VarAssignment >> '}';
神奇之处
我们如何获取与节点相关联的源位置信息？
auto set_location_info = annotate(_val, _1, _3);
on_success(Identifier, set_location_info);
on_success(VarAssignment, set_location_info);
on_success(SourceCode, set_location_info);
现在，“annotate”只是一个可调用对象的简化版本，定义如下：
template<typename It>
struct annotation_f {
typedef void result_type;
annotation_f(It first) : first(first) {}
It const first;
template<typename Val, typename First, typename Last>
void operator()(Val& v, First f, Last l) const {
do_annotate(v, f, l, first);
}
private:
void static do_annotate(ast::LocationInfo& li, It f, It l, It first) {
using std::distance;
li.line = get_line(f);
li.column = get_column(first, f);
li.length = distance(f, l);
}
static void do_annotate(...) { }
};
由于
get_column 的工作方式，这个函数对象是有状态的（因为它记住了开始迭代器）
[3]。正如你所看到的，
do_annotate 只接受从
LocationInfo 派生的任何内容。
现在，来证明一下：
std::string const content = "function FuncName_1 {\n var Var_1 = 3;\n var Var_2 = 4; }";
pos_iterator_t first(content.begin()), iter = first, last(content.end());
ParseGrammar<pos_iterator_t> resolver(first);
ast::SourceCode program;
bool ok = phrase_parse(iter,
last,
resolver,
qi::space,
program);
std::cout << std::boolalpha;
std::cout << "ok : " << ok << std::endl;
std::cout << "full: " << (iter == last) << std::endl;
if(ok && iter == last)
{
std::cout << "OK: Parsing fully succeeded\n\n";
std::cout << "Function name: " << program.function.name << " (see L" << program.printLoc() << ")\n";
for (auto const& va : program.assignments)
std::cout << "variable " << va.id.name << " assigned value " << va.value << " at L" << va.printLoc() << "\n";
}
else
{
int line = get_line(iter);
int column = get_column(first, iter);
std::cout << "-------------------------\n";
std::cout << "ERROR: Parsing failed or not complete\n";
std::cout << "stopped at: " << line << ":" << column << "\n";
std::cout << "remaining: '" << std::string(iter, last) << "'\n";
std::cout << "-------------------------\n";
}
这会打印出：
ok : true
full: true
OK: Parsing fully succeeded
Function name: FuncName_1 (see L1:1:56)
variable Var_1 assigned value 3 at L2:3:14
variable Var_2 assigned value 4 at L3:3:15
完整演示程序
在Coliru上实时查看
同时还展示了：
error handling, e.g.:
Error: expecting "=" in line 3:
var Var_2 - 4; }
^---- here
ok : false
full: false
-------------------------
ERROR: Parsing failed or not complete
stopped at: 1:1
remaining: 'function FuncName_1 {
var Var_1 = 3;
var Var_2 - 4; }'
-------------------------
BOOST_SPIRIT_DEBUG macros
- A bit of a hacky way to conveniently stream the
LocationInfo part of any AST node, sorry :)
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/support_line_pos_iterator.hpp>
#include <iomanip>
namespace qi = boost::spirit::qi;
namespace phx= boost::phoenix;
typedef boost::spirit::line_pos_iterator<std::string::const_iterator> pos_iterator_t;
namespace ast
{
namespace manip { struct LocationInfoPrinter; }
struct LocationInfo {
unsigned line, column, length;
manip::LocationInfoPrinter printLoc() const;
};
struct Identifier : LocationInfo {
std::string name;
};
struct VarAssignment : LocationInfo {
Identifier id;
int value;
};
struct SourceCode : LocationInfo {
Identifier function;
std::vector<VarAssignment> assignments;
};
namespace manip {
struct LocationInfoPrinter {
LocationInfoPrinter(LocationInfo const& ref) : ref(ref) {}
LocationInfo const& ref;
friend std::ostream& operator<<(std::ostream& os, LocationInfoPrinter const& lip) {
return os << lip.ref.line << ':' << lip.ref.column << ':' << lip.ref.length;
}
};
}
manip::LocationInfoPrinter LocationInfo::printLoc() const { return { *this }; }
}
BOOST_FUSION_ADAPT_STRUCT(ast::Identifier, (std::string, name))
BOOST_FUSION_ADAPT_STRUCT(ast::VarAssignment, (ast::Identifier, id)(int, value))
BOOST_FUSION_ADAPT_STRUCT(ast::SourceCode, (ast::Identifier, function)(std::vector<ast::VarAssignment>, assignments))
struct error_handler_f {
typedef qi::error_handler_result result_type;
template<typename T1, typename T2, typename T3, typename T4>
qi::error_handler_result operator()(T1 b, T2 e, T3 where, T4 const& what) const {
std::cerr << "Error: expecting " << what << " in line " << get_line(where) << ": \n"
<< std::string(b,e) << "\n"
<< std::setw(std::distance(b, where)) << '^' << "---- here\n";
return qi::fail;
}
};
template<typename It>
struct annotation_f {
typedef void result_type;
annotation_f(It first) : first(first) {}
It const first;
template<typename Val, typename First, typename Last>
void operator()(Val& v, First f, Last l) const {
do_annotate(v, f, l, first);
}
private:
void static do_annotate(ast::LocationInfo& li, It f, It l, It first) {
using std::distance;
li.line = get_line(f);
li.column = get_column(first, f);
li.length = distance(f, l);
}
static void do_annotate(...) {}
};
template<typename Iterator=pos_iterator_t, typename Skipper=qi::space_type>
struct ParseGrammar: public qi::grammar<Iterator, ast::SourceCode(), Skipper>
{
ParseGrammar(Iterator first) :
ParseGrammar::base_type(SourceCode),
annotate(first)
{
using namespace qi;
KeywordFunction = lit("function");
KeywordVar = lit("var");
SemiColon = lit(';');
Identifier = as_string [ alpha >> *(alnum | char_("_")) ];
VarAssignment = KeywordVar > Identifier > '=' > int_ > SemiColon;
SourceCode = KeywordFunction >> Identifier >> '{' >> *VarAssignment >> '}';
on_error<fail>(VarAssignment, handler(_1, _2, _3, _4));
on_error<fail>(SourceCode, handler(_1, _2, _3, _4));
auto set_location_info = annotate(_val, _1, _3);
on_success(Identifier, set_location_info);
on_success(VarAssignment, set_location_info);
on_success(SourceCode, set_location_info);
BOOST_SPIRIT_DEBUG_NODES((KeywordFunction)(KeywordVar)(SemiColon)(Identifier)(VarAssignment)(SourceCode))
}
phx::function<error_handler_f> handler;
phx::function<annotation_f<Iterator>> annotate;
qi::rule<Iterator, ast::SourceCode(), Skipper> SourceCode;
qi::rule<Iterator, ast::VarAssignment(), Skipper> VarAssignment;
qi::rule<Iterator, ast::Identifier()> Identifier;
qi::rule<Iterator> KeywordFunction, KeywordVar, SemiColon;
};
int main()
{
std::string const content = "function FuncName_1 {\n var Var_1 = 3;\n var Var_2 - 4; }";
pos_iterator_t first(content.begin()), iter = first, last(content.end());
ParseGrammar<pos_iterator_t> resolver(first);
ast::SourceCode program;
bool ok = phrase_parse(iter,
last,
resolver,
qi::space,
program);
std::cout << std::boolalpha;
std::cout << "ok : " << ok << std::endl;
std::cout << "full: " << (iter == last) << std::endl;
if(ok && iter == last)
{
std::cout << "OK: Parsing fully succeeded\n\n";
std::cout << "Function name: " << program.function.name << " (see L" << program.printLoc() << ")\n";
for (auto const& va : program.assignments)
std::cout << "variable " << va.id.name << " assigned value " << va.value << " at L" << va.printLoc() << "\n";
}
else
{
int line = get_line(iter);
int column = get_column(first, iter);
std::cout << "-------------------------\n";
std::cout << "ERROR: Parsing failed or not complete\n";
std::cout << "stopped at: " << line << ":" << column << "\n";
std::cout << "remaining: '" << std::string(iter, last) << "'\n";
std::cout << "-------------------------\n";
}
return 0;
}
[1] 遗憾的是，除了魔术范例外，这些内容并未得到充分记录。
[2] 好吧，我使用as_string来获得适当的Identifier赋值，而不需要太多的工作。
[3] 在性能方面可能有更智能的方式，但现在让我们保持简单。
utree，它被广泛认为是一个不错的实验，但已经不再得到精神开发者的支持。引用一位开发者的话：“吸引人的地方在于只有一种AST类型需要处理，但这也是它的弱点：一种大小适合所有的方法几乎总是不好的。”（更多上下文请参见 [spirit-general] 邮件列表） - sehephx::ref()和/或qi::locals（SO搜索可能会找到使用示例）。 - sehe