manopapad/proper — pull request #67 by fredrikelinder (2013-03-27 01:59:48+00:00)
Title: No call to next_state if postcondition returns false

In execution phase:

command execution loop
1 - check precondition
2 - evaluate the command
3 - check postcondition
4 - run next_state only if postcondition returned 'true'