How to use expression trees in PHP?

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)

An example would be:

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

Where:

• * = 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)

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

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

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

2 x * 3 5 * + 6 9 + -

Explained:

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

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

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