Flexible Logic is the fanciest-schmanciest feature of rusEfi.
Flexible Logic allows advanced users to get unprecedented level of configurability for custom outputs and engine control.
Fuel pump is already using this mechanism - see https://svn.code.sf.net/p/rusefi/code/trunk/firmware/controllers/core/le_functions.h
Here's a command to try:
eval "2 3 +"
See https://svn.code.sf.net/p/rusefi/code/trunk/firmware/controllers/core/le_functions.cpp for list of available methods