如何在PHP中使用表达式树? [英] How to use expression trees in PHP?

问题描述

我目前正在编写一个可解决方程式的PHP程序.我已将输入方程式分成一个数组，以便数组中的每一行都包含一个项. (因此[0] ="+ 5x"，[1] ="="，[2] ="-5"，[3] ="+10".这只是一个基本等式.脚本还对以下内容进行了划分是()中的子数组，例如2x +(5-3x)= 3(x + 1)[0] ="+ 2 * x"，[1] = array([0] ="+5" ....

I'm currently making a PHP-program that solves equations. I've divided the input equation into an array so that each line in the array contains one term. (So. [0] = "+5x", [1] = "=", [2] = "-5", [3] = "+10". This is just a basic equation. The script also divides what is in () into sub-arrays. So for example 2x+(5-3x)=3(x+1) [0] = "+2*x", [1] = array([0] = "+5"....

但是，我发现表达式树非常适合在此方程式求解器中使用.我已经搜索了整个互联网来学习它，但是找不到任何用PHP解释它的网站(我知道PHP OOP.).例如，在C语言中有很多页面对其进行了解释，但是据我所知，PHP毫无帮助，因为我不理解示例代码.

However, I discovered expression trees that is the perfect thing to use in this equation-solver. I've searched the whole internet to learn it, but I can't find any websites that explain it in PHP (I know PHP OOP.). There are lots of pages explaining them in for example C, but as I only know PHP, that is of no help, because I don't understand the example code.

任何人都可以在PHP中解释有关表达式树的所有内容以及一些实际的示例代码吗?

Can anyone here explain everything about expression trees in PHP and some practical example code?

推荐答案

这是算法描述.您可以在PHP中实现此功能.我认为没有人已经在PHP中实现了这一点(并将其作为开源分发)

Here is the algorithm described. you can implement this in PHP. I don't think anyone already implemented this in PHP (and distribute it as open source)

一个例子是:

2*x+3*5-(6+9) = 0

位置:

• * =优先级2
• + =优先级1
• ( =将标志的优先级提高10
• +(秒+)=优先级11
• ) =会将标志的优先级降低10
• = =在这种情况下，它表明还有另一个表达式(0)

• * = priority 2
• + = priority 1
• ( = will increase priority of signs by 10
• + (second +) = priority 11
• ) = will decrease priority of signs by 10
• = = in this case it is showing that there is another expression (0)

最高优先级是最重要的-您首先需要做的

The highest priority is the most important - the one you need to do first

使用这些规则，您可以创建一个表达式树...

Using these rules you can create an expression tree...

...您必须先创建表达式然后进行解释的一种方式是:

So.. a way in which you have to create the expression and then interpret is:

2 x * 3 5 * + 6 9 + -

解释:

• 2 * x | (1)
• 3 * 5 | (2)
• (1) + (2) | (3)
• 6 + 9 | (4)
• (3) - (4) = final

• 2 * x | (1)
• 3 * 5 | (2)
• (1) + (2) | (3)
• 6 + 9 | (4)
• (3) - (4) = final

我不记得是怎么写树的，我在计算机科学专业的课程中是这样做的，但是它是这样的:

I don't remember exactly how to write a tree I did this to a course in Computer Science but it was something like this:

                                     -
                                /         \
                                E         (E)
                                |          +
                                +         / \
                             /    \      6   9
                            E      E        
                            |      |    
                            *      *
                           / \    / \    
                          T   E   T  E
                          |   |   |  |
                          2   T   3  T
                              |      |
                              x      5

现在，您必须为此创建自己的解释器.您可以使用解释器模式: PHP解释器

Now you have to create your own interpreter for this. You can use the interpreter pattern: PHP Interpreter

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