My review of the Fusion library follows, but I'll spoil the ending now: I vote to accept Fusion into Boost. I was very interested to look into this library. I've found heterogeneous sequences to be extremely interesting and, in some cases, precisely the right answer. I've had to write about 1/3 to 1/2 of the heterogeneous algorithms provided by Fusion at various times, time which could have been saved and code that could have been cleaner if Fusion was around. So, I'm quite familiar with heterogeneous containers and algorithms. I was not able to review the library in-depth, unfortunately, but I'm itching to get my fingers on it when time allows. So, what follows is really just a bunch of minor nits from reading the documentation. Overall: - I'm not a fan of naming libraries anything but what they do. "Fusion" makes sense when you understand the context, but nobody searching through the list of libraries will see "Fusion" and think "AHA! That's what I need". Alas, I don't have a name in mind. Description: - Spelling error: "hetrogenous" Introduction: - Parts of the introduction are a bit too colloquial for my taste, in particular, the paragraph. "Hmmm, kinda reminds us of STL right? Right! Can you imagine how it would be like if you used STL without the algorithms? Everyone will have to reinvent their own algorithm wheels." I'd rather see them written in a more direct manner. Not that I prefer boring, but at some point the whimsical writing trivializes the library. Top of the Iceberg: - In the [1] footnote, spelling error: "Orgainization" Support: tag_of: I believe I understand the usefulness of this trait, but only because I understand tag dispatching already. Could the description be expanded a little, to at least say that tags uniquely identify the kind of sequence or iterator, e.g., list, map, etc.? category_of: I'm not keen on using the same trait (category_of) for two different kinds of entities (sequences and iterators). Traits classes should be tied to a particular concept, so I'd much rather see separate "iterator_category" and "sequence_category" metafunctions. pair: I tripped over the name of this entity a bit. It's a little odd to have a "pair" with only one kind of data. I guess I'd feel better if this were called "keyed_value" or "key_value", because it's easier for me to copy with a typed key than it us for me to have a pair that's very different from std::pair. Iterators: distance: Is the return type of distance(i, j) "int" or "convertible to int"? I could imagine that in many cases it could be an integral_constant<int, N>... It looks like Joel and Dan did a great job. Cheers, Doug