More missing params.
More missing params.

The next big thing is TraverseMsg, which is actually a bit tricky; I'm
not sure we can provide instances for these without significantly
reworking things, because TraverseMsg is defined on a type of kind
* -> *, but we'd also need to thread through the msg to each parameter.

I'm not sure we actually need these though; maybe we can just punt?

zenhack/haskell-capnp