Previously, expressions like:

`@if(status,\nLEFT(status, 2),\nfalse)`

would error out due to evaluating all arguments, even when not needed. This behavior prevented conditional checks like "if X is nil, do this otherwise do that".

With this change, argument evaluation is fully delegated to each function, allowing proper conditional checks. The custom callback function is now set as a custom context attribute, enabling nested functions to use it as needed.

…-in-advance