Prerequisities

Library for evaluating prerequisites writen in simple infix language.

Documentation

About

This library evaluates simple c-like logical expressions with given variables. It was made for MineHub academys prerequisites.

Syntax

As previously mentioned, it uses c-like logical expression syntax.

Variables

Variable names can contain every character except those: ()|&! - these are reserved for other syntax. Variables can be only boolean and will be loaded from eval function. See evaluation

In examples we would use true and false to make it simpler, but you can use any variable name you want, as long as it doesn't contain reserved words.

Operators

You can use operators or (||) with and (&&), where and has bigger priority, meaning that

true || true && false

would evaluate as true, instead of false.

Groups

To change priority, you can use groups (just put it in brackets). So this

(true || false ) && false

would evaluate as false

Negation

We can also negate variables and groups:

!true

would evaluate as false, and

!(true || false)

would also evaluate as false.

Everything is expression!

Everything is expression, so you can do stuff like:

(true || (false || true)) && (!(true || (false || true)) && false)

Formal definition

TODO maybe its not correct

<variable> ::= [^\s\(\)\|&!]+
<expression> ::= <variable>
<expression> ::= <expression>"||"<expression>
<expression> ::= <expression>"&&"<expression>
<expression> ::= "("<expression>")"
<expression> ::= "!"<expression>

Evaluation

To evaluate string, simply create instance of \MineHub\Prerequisities\Evaluator and use eval method. This method takes code and array of variables:

$evaluator = new Evaluator();
$evaluator->eval('!(!foo || bar) && (foo && !bar)', ['foo' => true, 'bar' => false]); // returns true