php-formula-interpreter

A formula interpreter for php

Why this library ?

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.

Installing

Use Composer to install it:

composer require khumbal/php-formula-interpreter

How does it work ?

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

Using operators

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)'

Comparison operators

Supported comparison operators are =, !=, <>, >=, >, <=, '<'.

'1 = 1' //true
'1 != 1' //false
'1 != 2' //true
'1 < 2' //true

Boolean operators

Supported boolean operators are AND and OR.

'(4 > 0) AND (3 > 2)' //true
'(4 > 0) AND (3 < 2)' //false
'(4 > 0) OR (3 < 2)' //true
'(4 < 0) AND (3 < 2)' //false

Future operators

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

Using variables

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 = [
   'price' => 40.2,
   'rate' => 12.8
];

$executable->run($variables);

Variables now supports dot . as the name.

$variables = [
   'user.name' => 'John Doe'
   'user.age' => '23'
];

$executable->run($variables);

String support

Variables can contain string. Use double quote (") for denote a string.

'a = "Hello world"'

Using functions

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)'

Custom functions

Now function can be added before compiling should you want to add more variables.

$compiler = new Compiler();
$compiler->registerFunction('foobar', function ($a, $b) {
    return $a + $b;
});
$executable = $compiler->compile("foobar(foo, bar)");
$params = [
    'foo' => 1,
    'bar' => 2
];
$executable->run($params);

Listing parameters

You can get a list of all variables that must be provided to the run() method in order to run the executable:

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

print_r($executable->getParameters());

This will output:

    Array
    (
        [0] => foo
        [0] => bar
    )