Dynamic logical expression parsing/evaluation in PHP?

Question

I have a need to evaluate user-defined logical expressions of arbitrary complexity on some PHP pages. Assuming that form fields are the primary variables, it would need to:

• substitute"varibles" for form fields values;
• handle comparison operators, minimally ==, <, <=, >= and > by symbol, name (eg eq, lt, le, ge, gt respectively);
• handle boolean operators not, and, or and possibly xor by name, symbol (eg !, &&, || and ^^ respectively);
• handle literal values for strings and numbers;
• be plaintext not XML (eg "firstname == '' or lastname == ''); and
• be reasonably performant.

Now in years gone by I've written recursive descent parsers that could build an expression tree and do this kind of thing but thats not a task I'm relishing in PHP so I'm hoping there are things out there that will at least get me some of the way there.

Suggestions?

Answer 1

Check create_function, it creates an anonymous function from the string parameters passed, I'm not sure about its performance, but it's very flexible...

Answer 2

Much time has gone by since this question was asked, and I happened to be looking for an expression parser for php. I chose to use the ExpressionLanguage component from Symfony 2.4. It can be installed with no dependencies from composer via packagist.

composer require symfony/expression-language