short introduction

1. Interpreter
2. Introduction
3. Error messages
4. Example programs
Short introduction to the Janus interpreter
This is not a description of the semantics of Janus (see [1]) or a manual to Janus
(see [2]), but a introduction to this implementation of Janus, which is based on [1].

Compared to the semantics from [1] three keywords have been added error, write and read,
which ease the program development.

  error id, this statement raises an error with a string argument.
  write var, this statement outputs the variable which is given as argument.
  read var, this statement has no effect at the moment.

Numbers in the interval [2³¹, 2³²-1] represent negative numbers in the interval
[-2³¹-1, -1]. Thus the biggest positive number plus one becomes the smallest negative
number. If you write a number which is bigger than 2³² it will be converted by modulo 2³².

The interpreter starts by executing the procedure called main. If this procedure does
not exist the last procedure in the program will be executed.

References
[1] Yokoyama, T. and Glück, R. 2007. A reversible programming language and its invertible
self-interpreter. In Proceedings of the 2007 ACM SIGPLAN Symposium on Partial Evaluation
and Semantics-Based Program Manipulation (Nice, France, January 15 - 16, 2007). PEPM '07.
ACM Press, New York, NY, 144-153. DOI= http://doi.acm.org/10.1145/1244381.1244404

[2] C. Lutz. Janus: a time-reversible language. A letter to Landauer.
http://www.cise.ufl.edu/~mpf/rc/janus.html, 1986.