A formula interpreter for php

Some user could wants to perform a simple calculation and being able to change it as much as he can. Before using a library, you could use the eval function. But this method has two major drawbacks :

• Security. A php script is being evaluated by the eval function. Php is a very powerful language, perhaps too powerful for a user especially when the user wants to inject malicious code.

• Complexity. Php is also complex for someone who doesn't understand programming language. It could be nice to interpret an excel-like formula instead.

First, create an instance of FormulaInterpreter\Compiler

$compiler = new FormulaInterpreter\Compiler();

Then use the compile()method to parse the formula you want to interpret. It will return an instance of FormulaInterpreter\Executable :

$executable = $compiler->compile('2 + 2');

Finally run the formula from the executable :

$result = $executable->run();
// $result equals 4

Operator multiplication (*) and division () are being evaluted first, then addition (+) and subtraction (-)

You can also force the prioriry of an expression by using parentheses like this

'2 * (3 + 2)'

You can use as many parentheses as you like.

'2 * (2 * (3 + 2 * (3 + 2)) + 2)'

Others operators like modulo, power, etc. will be implemented in the future as functions.

A variable is just a word inside your formula like this :

'price * rate / 100'

Just before executing a formula, make sure to inject all the required variables in an array

$variables = array(
   'price' => 40.2,
   'rate' => 12.8
);

$executable->run($variables);

Here is an example of expression using a function :

   'cos(0)'

Available functions : pi, pow, cos, sin, sqrt & modulo

You can embed functions as much as you like

   'pow(sqrt(4), 2)'