I’ve emailed it back to Andreas. My own version of pplFile redirects cerr to ostringstream instead of cout, then captures it, later it’s parsed by three_fourths in The Perp System -- since ngram -debug 1 outputs teh perplexities of the sentences on the 3rd, and then each 4th line after that.

I’m creating LM clients inside C++ and return integer handles to OCaml; one’s supposed to call lm_destroy for every lm_create, and in reverse order, and no creations after deletions. This corresponds to my use case, but surely can be generalized for better bindings, and switched from static LMClient *clients[] to std::vector<LMClient*>.