Parse Math Expression in PHP

问题:

I'm currently trying to parse math expression into expression tree. But I'm stuck on the stage where I need to implement functions and negates. I don't understand logic to do it using Shunting-Yard algorithm.

What I currently want to do is to support

• Negates, like -(x+5)
• Function calls, like min(x,y)
• Power just after function name, like cos^2(x)
• Implicit multiplication, like 2x is same as 2*x
• Scientific notation
• Constants e and pi

Can somebody tell me hints how to implement this?

回答1:

An working, PSR-0 compatible implementation of the shunting yard algorithm can be found here: https://github.com/andig/php-shunting-yard/tree/dev. It supports constants, custom functions etc.