1. DESCRIPTION Levy is a simple implementation of Paul Levy's call-by-push-value language. The implementation contains a parser, type-checker, and an interpreter. It is part of the PL Zoo, see http://math.andrej.com/plzoo/ The language has the following features: * integers with arithmetical operations *, +, - * booleans with conditional statements and comparison =, < of integers * functions * general recursion (fixpoint operator) * call-by-push-value features: return, thunk, force, sequence, and let binding See the file example.levy for concrete syntax. The language is different enough from standard functional languages that you will not be able to guess how it works without reading about cally-by-push-value first. A good place to start is Paul Levy's FAQ at http://www.cs.bham.ac.uk/~pbl/cbpv.html 2. AUTHOR The authors of the program are Matija Pretnar <matija@pretnar.info>, and Andrej Bauer <Andrej.Bauer@andrej.com>, with modifications by Robert Simmons <robsimmons@gmail.com>. Emacs mode by Ben Mosley. See the file COPYRIGHT.txt for license information. 3. REQUIREMENTS You need Objective Caml, http://caml.inria.fr/ version 3.10 or higher. If you have an older version of Objective Caml you can still compile the code by hand. A simple emacs highlighting mode for Levy is included; you can include it by adding the following text to your .emacs file, changing the levy-root directory to wherever the code for Levy was placed. ;; Setup for levy-mode (setq levy-root "/home/hqbovik/levy/") (load (concat levy-root "levy.el")) (add-to-list 'auto-mode-alist '("\\.levy\\'" . levy-mode)) 4. COMPILATION To compile the program run the command make For the native code version run make native If you do not have the make utility, run ocamlbuild levy.byte 5. USAGE First compile the program. You may then run the interpreter with ./levy.byte If you built the native code version, this would be ./levy.native The file example.levy contains examples that explain the concrete syntax. You can load it and try it as follows: $ ./levy.byte example.levy