在C ++中模拟ML风格模式匹配 [英] Simulating ML-style pattern matching in C++
问题描述
标题几乎全部,我将如何去模拟在C ++中的ML风格模式匹配,例如;
The title says pretty much all, how would I go about simulating ML-style pattern matching in C++, that is for instance;
Statement *stm;
match(typeof(stm))
{
case IfThen: ...
case IfThenElse: ...
case While: ...
...
}
其中'IfThen','IfThenElse'和'While'继承自'Statement'的类
Where 'IfThen', 'IfThenElse' and 'While' are classes which inherit from 'Statement'
推荐答案
C ++委员会最近有一篇论文描述了一个库, :
There was a paper in the C++ committee recently which describe a library that allow to do just that:
Stroustup,Dos Reis和Solodkyy为C ++打开和有效的类型切换
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3449.pdf
Open and Efficient Type Switch for C++ by Stroustup, Dos Reis and Solodkyy
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3449.pdf
指向包含源代码的页面的链接:
https://parasol.tamu.edu/~yuriys/pm/
A link to a page with source code :
https://parasol.tamu.edu/~yuriys/pm/
免责声明:我没有尝试编译或
Disclaimer : I didn't try to compile or use this library, but it seem to fit your question.
以下是图书馆提供的示例之一:
Here is one of the sample provided by the library :
#include <utility>
#include "match.hpp" // Support for Match statement
//------------------------------------------------------------------------------
typedef std::pair<double,double> loc;
// An Algebraic Data Type implemented through inheritance
struct Shape
{
virtual ~Shape() {}
};
struct Circle : Shape
{
Circle(const loc& c, const double& r) : center(c), radius(r) {}
loc center;
double radius;
};
struct Square : Shape
{
Square(const loc& c, const double& s) : upper_left(c), side(s) {}
loc upper_left;
double side;
};
struct Triangle : Shape
{
Triangle(const loc& a, const loc& b, const loc& c) : first(a), second(b), third(c) {}
loc first;
loc second;
loc third;
};
//------------------------------------------------------------------------------
loc point_within(const Shape* shape)
{
Match(shape)
{
Case(Circle) return matched->center;
Case(Square) return matched->upper_left;
Case(Triangle) return matched->first;
Otherwise() return loc(0,0);
}
EndMatch
}
int main()
{
point_within(new Triangle(loc(0,0),loc(1,0),loc(0,1)));
point_within(new Square(loc(1,0),1));
point_within(new Circle(loc(0,0),1));
}
这是令人惊讶的干净!
This is surprisingly clean !
图书馆的内部结构看起来有点可怕。我快速浏览一下,似乎有很多先进的宏和元程序设计。
The internals of the library looks a bit more scary though. I did a quick glance and there seems to be quite a lot of advanced macro and meta-programing.
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