Hi everyone, For those who don't remember, I'm an undergrad stutent doing an internship about writing textbook interpreters and turn them into JITing VMs using the pypy translation toolchaine. I'm facing a little problem I don't understand. I've written a version of my interpreter using Map as described in the paper Runtime feedback (http://dl.acm.org/citation.cfm?id=2069181 ) to replace dictionnaries I used to use, but when I try to translate I get "assert v.concretetype is lltype.Void" Assertion Error I know this error, I already faced it and going into Pypy's code, I found out this was about the order of variables in jitdriver.jit_merge_point and jitdriver.can_enter_jit . Previously changing approprietly the order of variables solved the problem, but this time even bruteforcely testing every permutation didn't solve the problem and I'm stuck. If you could help, I'll be very grateful. You can find the file here: https://github.com/zebign1/RPython-internship/blob/master/Interpreters/ifF1W... Map implementation can be found in the file treeClass.py in the parent directory, all along with the parser file. Thanks for your help Leonard.