There seems to be limitations (or problems) with compilation of pattern matching.

https://github.com/svenssonjoel/Sense-VM/blob/master/frontend/CamIoT/testcases/bad6.cam

https://github.com/svenssonjoel/Sense-VM/blob/master/frontend/CamIoT/testcases/bad7.cam

bad6 is an example of a program that may be generating faulty bytecode.
bad7 is a case of pattern matching compilation not working.
I think the line of code: 'foo Empty _ _ _ = ...' is where the compiler gives up.