Detect circular lists in LENGTH
It would be nice LENGTH of lists could detect circular lists. Currently, we have assembly VOPs to compute LENGTH (… really). It seems to me we could make everything simpler by instead calling to a regular CL function (e.g. %list-length) via a deftransform. There doesn't even have to be a huge penalty to detect circular lists: we can easily call out to CL:LIST-LENGTH once the length is greater than a couple thousand conses.