用Spirit作为AST节点的虚拟类 [英] Virtual classes as AST nodes with Spirit
问题描述
我正在与一位朋友一起为一种语言进行口译,我们从一个决定开始,我猜那不是那么明智:我们首先确定所有要执行的元素(实际上是一棵由不同类组成的树);但是现在来看助推器示例,我对如何将两者合并感到非常困惑。我知道从(语法)开始,我知道要到达(相互拥有的实例化课程),我不知道如何到达。
我们从没有变量的表达式开始,因此我们看了精神计算器示例;但是我不知道何时实例化元素。
表达式项示例:
namespace exp
{
class op
{
private:
public:
virtual double exec(function_scope& fs);
};
类操作数:public op
{
private:
double value;
public:
操作数(双值);
double exec(function_scope& fs);
};
class op_bin:公共操作
{
私人:
公共:
op * ll;
op * rr;
op_bin(op * ll,op * rr);
〜op_bin();
};
名称空间bin
{
类总和:public op_bin
{
public:
sum(op * ll,op * rr);
double exec(function_scope& fs);
};
}
}
忽略exec函数,它在运行时使用。 / p>
例如,代码5 +(2 + 1)的最终结果应为:
new exp :: bin :: sum(new exp :: operand(5),new exp :: bin :: sum(new exp :: operand(2),new exp :: operand(1 ))
一旦我了解了我实际上已完成的操作。
好吧,我打算写出您的问题出了什么问题,但是我去证明自己,做出想要的事情并不难。
几个关键点:
- 我稍加修改,重命名并扩展了ast使其发挥作用并实际显示某些东西。
-
Spirit规则出于某种原因制作了属性的副本(我认为这是一个错误),因此我针对(在1.70中修复)unique_ptr
具有特征。 - 我不确定
x3是否: :忽略
实际上是必需的(您可以删除除最后一个以外的所有内容,它将进行编译),但这似乎是Spirit中的另一个错误。 -
make_node
看起来不可靠,并且可能以令人惊讶的方式破坏,您可以根据需要将其拆分为单独的一元/二进制节点创建者。 - 有时,您将希望为您的ast节点创建使用状态分配器,将分配器注入解析器上下文中应该非常简单。我将它留给您作为练习。
解析器:
#include< boost / spirit / home / x3.hpp>
#include< memory>
#include< iostream>
命名空间ast
{
类表达式
{受保护的
:
expression()=默认值;
public:
virtual〜expression()=默认值;
expression(expression&& other)=删除;
表达式和运算符=(表达式&其他)=删除;
虚拟无效打印(std :: ostream&)const = 0;
朋友std :: ostream&运算符<(std :: ostream& os,表达式const&节点)
{
node.print(os);
return os;
}
};
类操作数:公共表达式
{
double value_;
public:
constexpr操作数(双值):value_ {value} {}
void print(std :: ostream& os)const替代{os<<值_; }
};
class op_bin:公共表达式
{受保护的
:
std :: unique_ptr< expression>左右_;
public:
op_bin(std :: unique_ptr< expression>左,std :: unique_ptr< expression>右)
:left_ {std :: move(left)}, right_ {std :: move(right)}
{}
op_bin(expression * left,expression * right)
:left_ {left},right_ {right}
{}
};
class plus:public op_bin
{
public:
使用op_bin :: op_bin;
void print(std :: ostream& os)const覆盖
{os<< ’(’<< * left_<< +<< * right_<<’)); }
};
类减去:public op_bin
{
public:
使用op_bin :: op_bin;
void print(std :: ostream& os)const覆盖
{os<< ’(’<< * left_<<--<< * right_<<’)); }
};
class mul:public op_bin
{
public:
using op_bin :: op_bin;
void print(std :: ostream& os)const覆盖
{os<< ’(’<< * left_<< *<< * right_<<’)); }
};
class div:公共op_bin
{
public:
使用op_bin :: op_bin;
void print(std :: ostream& os)const覆盖
{os<< ’(’<< * left_<< /<< * right_<<’)); }
};
} //命名空间ast
命名空间语法
{
命名空间x3 = boost :: spirit :: x3;
模板< typename T>
struct make_node_
{
template< typename Context>
void operator()(上下文const& ctx)const
{
if constexpr(std :: is_convertible_v< decltype(x3 :: _ attr(ctx)),T>){
x3 :: _ val(ctx)= std :: make_unique< T(std :: move(x3 :: _ attr(ctx))));
}
else {
x3 :: _ val(ctx)= std :: make_unique< T>(std :: move(x3 :: _ val(ctx)),std :: move( x3 :: _ attr(ctx)));
}
}
};
模板< typename T>
constexpr make_node_< T> make_node {};
使用x3 :: double_;
使用x3 :: char_;
x3 :: rule< class expression_r,std :: unique_ptr< ast :: expression> ;, true> const表达式
x3 :: rule< class prec1_r,std :: unique_ptr< ast :: expression> ;, true> const prec1;
x3 :: rule< class prec0_r,std :: unique_ptr< ast :: expression> ;, true> const prec0;
auto const expression_def =
prec1
> *(x3 :: omit [('+'> prec1)[make_node< ast :: plus>]]
| x3 :: omit [('-'> prec1)[make_node< ast :: minus> ;]]
)
;
auto const prec1_def =
prec0
> *(x3 :: omit [('*'> prec0)[make_node< ast :: mul>]]
| x3 :: omit [(//> prec0)[make_node< ast :: div> ;]]
)
;
auto const prec0_def =
x3 :: omit [double_ [make_node< ast :: operand>]]
| ’(’>表达式>’)’
;
BOOST_SPIRIT_DEFINE(
表达式
,prec1
,prec0
);
} //名称空间语法
#if BOOST_VERSION< 107000
名称空间boost :: spirit :: x3 :: traits {
template< typename Attribute>
struct make_attribute< std :: unique_ptr< Attribute> ;, std :: unique_ptr< Attribute>
:make_attribute_base< std :: unique_ptr< Attribute>>
{
typedef std :: unique_ptr< Attribute>&类型;
typedef std :: unique_ptr< Attribute>&值类型;
};
} //命名空间boost :: spirit :: x3 :: traits
#endif
int main()
{
命名空间x3 = boost :: spirit :: x3;
std :: string s = 1 + 2 *(3-4)/ 5;
std :: unique_ptr< ast :: expression> expr;
if(auto iter = s.cbegin();!phrase_parse(iter,s.cend(),grammar :: expression,x3 :: space,expr)){
std :: cout< < 解析失败;
}
else {
if(iter!= s.cend())
std :: cout<< 部分解析;
std :: cout<< * expr<< ‘n’;
}
}
输出:
(1 +((2 *(3-4))/ 5))
i was working on an interpreter for a language with a friend, and we started with a decision I'm guessing wasn't that wise: we made all the elements for execution first (practically a tree made of different classes); but now looking at boost examples i get a lot confused about how to merge the two. I know what to start from (the grammar), i know what to reach (instantiated classes owning each other), i don't know how to reach it.
We started with expressions without variables, hence we looked at spirit calculator examples; but i don't understand when to instantiate elements.
Example of expression items:
namespace exp
{
class op
{
private:
public:
virtual double exec(function_scope &fs);
};
class operand : public op
{
private:
double value;
public:
operand(double value);
double exec(function_scope &fs);
};
class op_bin : public op
{
private:
public:
op * ll;
op* rr;
op_bin(op* ll, op* rr);
~op_bin();
};
namespace bin
{
class sum : public op_bin
{
public:
sum(op* ll, op* rr);
double exec(function_scope &fs);
};
}
}
Ignore the exec function, it's used at runtime.
For example the code 5 + (2 + 1) should result in a final equivalent of:
new exp::bin::sum(new exp::operand(5), new exp::bin::sum(new exp::operand(2), new exp::operand(1))
Once i understand how to do that I've practically done.
Well, I was going to write what's wrong with your question, but instead I went to prove myself that it is not that hard to make what you want.
Few keypoints:
- I slightly modified, renamed and extended your ast to make it work and to actually show something.
Spirit rules for some reason make copy of an attribute (I think it is a bug), so I workarounded this issue for(fixed in 1.70)unique_ptr
with a trait.- I am not sure if
x3::omit
is actually required there (you can remove all except the last and it will compile), but it looks like it is an another bug in Spirit. make_node
looks unreliable and may broke in surprising ways, you can split it into separate unary/binary node creators if you wish.- At some point you will want to use stateful allocator for your ast nodes creation, it should be very simple by injecting allocator into the parser context. I am leaving it for you as an exercise.
The parser:
#include <boost/spirit/home/x3.hpp>
#include <memory>
#include <iostream>
namespace ast
{
class expression
{
protected:
expression() = default;
public:
virtual ~expression() = default;
expression(expression&& other) = delete;
expression& operator=(expression&& other) = delete;
virtual void print(std::ostream&) const = 0;
friend std::ostream& operator<<(std::ostream& os, expression const& node)
{
node.print(os);
return os;
}
};
class operand : public expression
{
double value_;
public:
constexpr operand(double value) : value_{value} {}
void print(std::ostream& os) const override { os << value_; }
};
class op_bin : public expression
{
protected:
std::unique_ptr<expression> left_, right_;
public:
op_bin(std::unique_ptr<expression> left, std::unique_ptr<expression> right)
: left_{ std::move(left) }, right_{ std::move(right) }
{}
op_bin(expression * left, expression * right)
: left_{ left }, right_{ right }
{}
};
class plus : public op_bin
{
public:
using op_bin::op_bin;
void print(std::ostream& os) const override
{ os << '(' << *left_ << " + " << *right_ << ')'; }
};
class minus : public op_bin
{
public:
using op_bin::op_bin;
void print(std::ostream& os) const override
{ os << '(' << *left_ << " - " << *right_ << ')'; }
};
class mul : public op_bin
{
public:
using op_bin::op_bin;
void print(std::ostream& os) const override
{ os << '(' << *left_ << " * " << *right_ << ')'; }
};
class div : public op_bin
{
public:
using op_bin::op_bin;
void print(std::ostream& os) const override
{ os << '(' << *left_ << " / " << *right_ << ')'; }
};
} // namespace ast
namespace grammar
{
namespace x3 = boost::spirit::x3;
template <typename T>
struct make_node_
{
template <typename Context>
void operator()(Context const& ctx) const
{
if constexpr (std::is_convertible_v<decltype(x3::_attr(ctx)), T>) {
x3::_val(ctx) = std::make_unique<T>(std::move(x3::_attr(ctx)));
}
else {
x3::_val(ctx) = std::make_unique<T>(std::move(x3::_val(ctx)), std::move(x3::_attr(ctx)));
}
}
};
template <typename T>
constexpr make_node_<T> make_node{};
using x3::double_;
using x3::char_;
x3::rule<class expression_r, std::unique_ptr<ast::expression>, true> const expression;
x3::rule<class prec1_r, std::unique_ptr<ast::expression>, true> const prec1;
x3::rule<class prec0_r, std::unique_ptr<ast::expression>, true> const prec0;
auto const expression_def =
prec1
>> *( x3::omit[('+' > prec1)[make_node<ast::plus>]]
| x3::omit[('-' > prec1)[make_node<ast::minus>]]
)
;
auto const prec1_def =
prec0
>> *( x3::omit[('*' > prec0)[make_node<ast::mul>]]
| x3::omit[('/' > prec0)[make_node<ast::div>]]
)
;
auto const prec0_def =
x3::omit[double_[make_node<ast::operand>]]
| '(' > expression > ')'
;
BOOST_SPIRIT_DEFINE(
expression
, prec1
, prec0
);
} // namespace grammar
#if BOOST_VERSION < 107000
namespace boost::spirit::x3::traits {
template <typename Attribute>
struct make_attribute<std::unique_ptr<Attribute>, std::unique_ptr<Attribute>>
: make_attribute_base<std::unique_ptr<Attribute>>
{
typedef std::unique_ptr<Attribute>& type;
typedef std::unique_ptr<Attribute>& value_type;
};
} // namespace boost::spirit::x3::traits
#endif
int main()
{
namespace x3 = boost::spirit::x3;
std::string s = "1 + 2 * (3 - 4) / 5";
std::unique_ptr<ast::expression> expr;
if (auto iter = s.cbegin(); !phrase_parse(iter, s.cend(), grammar::expression, x3::space, expr)) {
std::cout << "parsing failed";
}
else {
if (iter != s.cend())
std::cout << "partially parsed\n";
std::cout << *expr << '\n';
}
}
Output:
(1 + ((2 * (3 - 4)) / 5))
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