My php string parser library provides an abstract mechanism to tokenize, parse and until compile any kind of scripts you want.
There are some implemented parsers ready to use for expressions.

$parser = new SimpleTokenParser();
print_r($parser->parseString("12 + 13 / 6"));

This list all parsed tokens.
Token parsing is done by php token_get_all function, but you can easy subclass a tokenizer to customize string tokenizing.

Install

PHP String Parser is a composer package. So you can simply install it by

$ composer require tasoft/php-string-parser

Now the library is available under namespace \TASoft\Parser...

Examples

The package tasoft/predicate uses this parser to create predicates from string.