Do you have a use case for this instance? I don't think I would ever want it. Also I think the behavior is too unspecified, and trying to specify it more precisely will inevitably lead to a much less useful instance. In this instance I might prefer we focus on problems we have already rather make new ones.
Also +1 for rotate acting like shift for infinite types, for the reasons Milan gave.
John L.
Thinking about this some more, I ran into something else to chew on.
It would seem to make a certain amount of sense to have
instance (Bits b) => Bits (Seq b)
with .&., .|., and xor defined using a zero-prepending zipWith variant.
but there are a few challenges relating to size. Specifically:
1. The specification indicates that finiteBitSize and bitSizeMaybe are
supposed to return a result based only on the type of their argument.
Clearly, that will not work for this.
2. There is no obviously correct size to use for zeroBits and bit.
One approach, of course, is to define something wonky like
newtype SeqN (n::Nat) a = SeqN (Seq a)
and then use
instance (Bits b) => Bits (SeqN n b)
but that gives a different, more limited type than one might expect.
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