Another interesting approach is 'success typing' in Erlang, as described in this elegant paper: http://user.it.uu.se/~tobiasl/publications/contracts.pdf http:/

Another interesting approach is 'success typing' in Erlang, as described in this elegant paper: http://user.it.uu.se/~tobiasl/publications/contracts.pdf http://user.it.uu.se/~tobiasl/publications/contracts.pdf Success typing is optionally refined through typespecs in the code and checked by the Dialyzer tool: http://www.erlang.org/doc/reference_manual/typespec.html http://www.erlang.org/doc/reference_manual/typespec.html http://learnyousomeerlang.com/dialyzer http://learnyousomeerlang.com/dialyzer Success typing is open to gradual typing of legacy code, as more typespecs are added, constraints gradually tighten, and Dialyzer finds the inconsistencies.