The previous add filter only supported numbers, whereas the django spec indicates that the values will be coerced to numbers, and if that fails added anyway (i.e., string/list concatenation). The change is slightly messy, but I believe is at least closer to the spec.
Updated add filter to match language spec
Hmm, OK. This behavior is poor API design but that is the fault of the Django spec. Please add unit tests (tests/src/erlydtl_unittests.erl) and I will merge this in.
Added unit tests for add filter
Agreed on the API design! I've added in unit tests for the various combinations, let me know if there's anything else you need. Great library, BTW :)