SLIP is a list processing computer programming language, invented by Joseph Weizenbaum in the 1960s.
It was first implemented as an extension to the Fortran programming language, and later embedded into MAD and ALGOL.
[3] In a nutshell, SLIP consisted of a set of FORTRAN "accessor" functions which operated on circular doubly linked lists with fixed-size data fields.
The header included a reference count field for garbage collection purposes.
The reader was essentially a state history stack—a good example of a memento pattern—where each cell pointed to the header of the list being read, the current position within the list being read, and the level or depth of the history stack.