     Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''.

     A copy of the license is also available from the Free Software Foundation Web site at http://www.gnu.org/licenses/fdl.html.

     Altenately, this document is also available under the Lesser General Public License, version 3 or later, as published by the Free Software Foundation.

     A copy of the license is also available from the Free Software Foundation Web site at http://www.gnu.org/licenses/lgpl.html.

8sync
*****

Copyright © 2015  Christopher Allan Webber cwebber@dustycloud.org

Introduction
************

8sync's goal is to make asynchronous programming easy. If you've worked with most other asynchronous programming environments, you know that it generally isn't. Usually asynchronous programming involves entering some sort of ``callback hell''. Some nicer environments like Asyncio for Python provide generator-based coroutines, but even these require a lot of work to carefully line up.

Coding in 8sync, on the other hand, looks almost entirely like coding anywhere else. This is because 8sync makes great use of a cool feature in Guile called ``delimited continuations'' to power natural-feeling coroutines. Because of this, you can invoke your asynchronous code with a small wrapper around it, and that code will pop off to complete whatever other task it needs to do, and resume your function when it's ready passing back the appropriate value. (No need to manually chain the coroutines together, and no callback hell at all!)

Now that's pretty cool!

Acknowledgements
****************

8sync has a number of inspirations:

  * asyncio (https://docs.python.org/3.5/library/asyncio.html) for Python provides a nice asynchronous programming environment, and makes great use of generator-style coroutines. It's a bit more difficult to work with than 8sync (or so thinks the author) because you have to ``line up'' the coroutines.

  * Sly (http://dthompson.us/pages/software/sly.html) by David Thompson is an awesome functional reactive game programming library for Guile. If you want to write graphical games, Sly is almost certainly a better choice than 8sync. Thanks to David for being very patient in explaining tough concepts; experience on hacking Sly greatly informed 8sync's development. (Check out Sly, it rocks!)

  * Reading SICP (https://mitpress.mit.edu/sicp/), particularly Chapter 3's writings on concurrent systems (https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-19.html#%_chap_3), greatly informed 8sync's design.

  * Finally, XUDD (https://docs.python.org/3.5/library/asyncio.html) was an earlier ``research project'' that preceeded 8sync. It attempted to bring an actor model system to Python. However, the author eventually grew frustrated with some of Python's limitations, fell in love with Guile, and well... now we have 8sync, which is much more general anyway.

The motivation to build 8sync came out of a conversation (https://lists.gnu.org/archive/html/guile-devel/2015-10/msg00015.html) at the FSF 30th party between Mark Weaver, David Thompson, Andrew Engelbrecht, and Christopher Allan Webber over how to build an asynchronous event loop for Guile and just what would be needed.

A little over a month after that, hacking on 8sync began!

8sync's license and general comments on copyleft
************************************************

8sync is released under the GNU LGPL (Lesser General Public License), version 3 or later, as published by the Free Software Foundation. The short version of this is that if you distribute a modifications to 8sync, whether alone or in some larger combination, must release the corresponding source code. A program which uses this library, if distributed without source code, must also allow relinking with a modified version of this library. In general, it is best to contribute them back to 8sync under the same terms; we'd appreciate any enhancements or fixes to be contributed upstream to 8sync itself. (This is an intentional oversimplification for brevity, please read the LGPL for the precise terms.)

This usage of the LGPL helps us ensure that 8sync and derivatives of 8sync as a library will remain free. Though it is not a requirement, we request you use 8sync to build free software rather than use it to contribute to the growing world of proprietary software.

The choice of the LGPL for 8sync was a strategic one, though in general, we encourage stronger copyleft. (For more thinking on this position, see Why you shouldn't use the Lesser GPL for your next library (https://www.gnu.org/licenses/why-not-lgpl.html).)

In particular, if you are building a library or application that uses 8sync in some useful way, consider releasing your program under the GNU GPL or GNU AGPL! In a world where more and more software is locked down, where software is used to restrict users, we could use every chance we can get to provide protections so that software which is free remains free, and encourages even more software freedom to be built upon it.

So to answer the question, ``Can I build a proprietary program on top of 8sync?'' our response is ``Yes, but please don't. Choose to release your software under a freedom-respecting license. And help us turn the tide towards greater software freedom... consider a strong copyleft license!''

Copying This Manual
*******************

This manual is licensed under the GNU Free Documentation License, with no invariant sections.  At your option, it is also available under the GNU Lesser General Public License, as published by the Free Software Foundation, version 3 or any later version.

GNU Free Documentation License
==============================

     [file fdl.texi not included]