The documented requirement of pop_back are wrong. The docs say that pop_back works on Forward Sequences, however the following does not compile: // ERROR fusion::list<int, int> l(1, 2); fusion::pop_back(l); The problem is that the implementation of pop_back uses prior, which only works on Bidirectional Sequences. That's merely a doc problem, but this is a more serious problem: // ERROR fusion::pop_back(fusion::pop_back( fusion::push_back(fusion::push_back(fusion::nil(), 1), 2))); A sequence created by push_back is a Forward Sequence, which means you can't call pop_back on it. I think that's a serious shortcoming. Fusion needs something like MPL's Back Extensible and Front Extensible concepts. http://www.boost.org/doc/libs/1_47_0/libs/mpl/doc/refmanual/back-extensible-... Unfortunately, this would likely require a redesign of the whole (push|pop)_(front|back) mechanism. -- Eric Niebler BoostPro Computing http://www.boostpro.com