How to check the security of user code before executing in eval?

Question

PHP

It is necessary to provide users of the online service with the ability to create formulas (arithmetic and logical operations, branching, variables are allowed).
To solve the problem, I suppose to run user code through eval, after checking for prohibited functions and expressions. We wrote the following regular expression to search for forbidden constructs in the code:
'/[^$\w]([a-zA-Z][\w_]+)|(\$this)/i'
Is such a check sufficient for the safety of running user code ? Maybe there are better solutions to the problem?

Answer 1

https://github.com/ziadoz/awesome-php#code-analysis

Answer 2

There is an option, of course. It's easier, but less correct. It is correct to write a parser for the syntax of your formulas, it should be primitive for you, judging by the conditions of the problem.