Cyclic lists

There is not much practical value in this, but it should be mentioned….

It is possible to create cyclic lists with SETF.

Printer can print safely cyclic lists, but reader does not recognize the notation.

In general, we recognize three kinds of cyclic phenomena:

• cdr cyclic
• car cyclic
• repeated sublists (not really cyclic, but can point to tail of higher list etc.)

Built-in functions should have safety for cyclic lists, so no infinite loops should happen in the C++ implementations.

Infinite loops can happen on the LabLISP level, but the processes can be killed.

! garbage collection cannot handle dropped cyclic list reference, will leak memory