Detecting circular structures (sometimes just called graphs), is a solved problem. The Lisp reader and printer even serialize them correctly: #1=(42 . #1#) make

Detecting circular structures (sometimes just called graphs), is a solved problem. The Lisp reader and printer even serialize them correctly: #1=(42 . #1#) makes a pair of two items. The first item is a 42 and the second is the pair itself. It sounds like whoever implemented this just didn't know what they were doing.