Why this does not work?

[akoSalman]

$instance->e('(2 + 2)');

It throws this error Undefined offset: -2. I think there is problems with parentheses with this class.

[vdomah]

did you find the fix for this problem? I'm facing the same issue

[optimistex]

@vdomah Try this: https://github.com/optimistex/math-expression There are some fixes and improvements