`length+``clist`procedureBoth

`length`and`length+`return the length of the argument. It is an error to pass a value to`length`which is not a proper list (finite and nil-terminated). In particular, this means an implementation may diverge or signal an error when`length`is applied to a circular list.`length+`, on the other hand, returns`#F`when applied to a circular list.The length of a proper list is a non-negative integer N such that

`cdr`applied N times to the list produces the empty list.