mes/doc/mes.texi

\input texinfo
@c -*- mode: texinfo; -*-

@c %**start of header
@setfilename mes.info
@documentencoding UTF-8
@settitle Mes Reference Manual
@c %**end of header

@include version.texi

@c Identifier of the OpenPGP key used to sign tarballs and such.
@set OPENPGP-SIGNING-KEY-ID 1A858392E331EAFDB8C27FFBF3C1A0D9C1D65273

@copying
Copyright @copyright{} 2018 Jan (janneke) Nieuwenhuizen@*

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''.
@end copying

@dircategory Bootstrapping
@direntry
* mes: (mes)Invoking mes.       Running Mes, a minimalist Guile lookalike.
* mescc: (mes)Invoking MesCC.   Running the MesCC bootstrap compiler.
@end direntry

@titlepage
@title Mes Reference Manual
@subtitle Full Source Bootstrapping of the GNU GuixSD Operating System
@author Jan (janneke) Nieuwenhuizen

@page
@vskip 0pt plus 1filll
Edition @value{EDITION} @*
@value{UPDATED} @*

@insertcopying
@end titlepage

@contents

@c *********************************************************************
@node Top
@top Mes

This document describes Mes version @value{VERSION}, a bootstrappable
Scheme interpreter and C compiler written for bootstrapping the GNU system.

@menu
* Introduction::                What is Mes about?
* Installation::                Installing Mes.
* Bootstrapping::               Would you strap my boots?
* Contributing::                Your help needed!
* Acknowledgments::             Thanks!
* GNU Free Documentation License::  The license of this manual.
* Concept Index::               Concepts.
* Programming Index::           Data types, functions, and variables.

@detailmenu
 --- The Detailed Node Listing ---

Software Freedom

* Reproducible Builds::         Reproducibility and free software.
* Bootstrappable Builds::       The freedom to build a software without binary seed.
* Full Source Bootstrap::       Software dependencies worthy of GNU.

Installation

* Regular Requirements::        Software needed to build and run Mes.
* Bootstrap Requirements::      Software needed to bootstrap Mes.
* Running the Test Suites::     Testing Mes.

Bootstrapping

* The Mes Bootstrap Process::   How Mes will make you yogurt from pure milk.
* Invoking Mes::                Running Mes, a minimalist Guile lookalike.
* Invoking MesCC::              Running the MesCC bootstrap compiler.

Invoking Mes

* Environment Variables::       If the bits won't change, change their habitat.

Invoking MesCC

* MesCC Environment Variables::  There's no NIX like POSIX.

Contributing

* Building from Git::           The latest and greatest.
* Running Mes From the Source Tree::  Hacker tricks.
* The Perfect Setup::           The right tools.
* Coding Style::                Hygiene of the contributor.
* Submitting Patches::          Share your work.

@end detailmenu
@end menu

@c *********************************************************************
@node Introduction
@chapter Introduction

@quotation
These were “Maxwell’s Equations of Software!”

@author Alan Kay
@end quotation

Mes@footnote{``Mes'' is an acronym for the Maxwell Equations of
Software.} consists of a mutual self-hosting Scheme interpreter
prototype written in C and a Nyacc-based (see @pxref{NYACC User's
Guide,,, nyacc-ug, NYACC User's Guide}) C compiler written in Scheme.

The Scheme interpreter @file{mes.c} is about 5000LOC of restricted C and
intended to be bootstrappable using a very simple C compiler.

@section Software Freedom
@cindex purpose
The four essential Freedoms of Software are at the core of our GNU
community.  Quoting the first freedom from
@url{https://www.gnu.org/philosophy/free-sw.html}

@quotation
The freedom to study how the program works, and change it so it does
your computing as you wish (freedom 1).  Access to the source code is a
precondition for this.
@end quotation

So we have access to the software, we have studied it, possibly modified
it, we built it and we installed it on a computer or some device.  How
can we trust that when we run the program we are indeed running the
untainted product of the source code that we studied?

@menu
* Reproducible Builds::         Reproducibility and free software.
* Bootstrappable Builds::       The freedom to build a software without binary seed.
* Full Source Bootstrap::       Software dependencies worthy of GNU.
@end menu

@node Reproducible Builds
@section Reproducible Builds

The current Reproducible Builds effort incubated in the Debian
project@footnote{http://debian.org} and was organized by Lunar.  Quoting
the @url{https://reproducible-builds.org/} website

@quotation
A build is reproducible if given the same source code, build environment
and build instructions, any party can recreate bit-by-bit identical
copies of all specified artifacts.
@end quotation

@subsection Can we trust our freedom?

Now consider the opposite, that a second build of a piece of source code
produces a different binary program.  Upon further investigation we
might find that the only difference is a timestamp that was embedded in
the binary, or perhaps the name of the directory it was built in.  Such
investigations can be nontrivial and are highly unpractical.  And what
if the binary difference is not so trivial, cannot be easily accounted
for?

A piece of software that cannot be built bit-by-bit reproducible is
probably not a good community member in the world of software freedom.
We think the importance of reproducibility should not be underestimated
largely because failing that precondition makes justifable trust in
binaries provided suspect at best and downright dangerous in reality.

It becomes clear that a bit-by-bit reproducible build of all our
sofwares is essential if we value our Freedom #1.

@subsection An Old Idea

The idea of reproducible builds is not very new.  It was implemented for
GNU tools in the early 1990s (which we learned, much later in 2017).  In
the Debian world it was mentioned first in 2000 and then more explicitly
in 2007 on
debian-devel@footnote{@url{https://lists.debian.org/debian-devel/2007/09/msg00746.html}}

@quotation
I think it would be really cool if the Debian policy required that
packages could be rebuild bit-identical from source.

@author Martin Uecker
@end quotation

@node Bootstrappable Builds
@section Bootstrappable Builds

Software distributions that take reproducible builds seriously are
currently shipping well over 90% reproducible packages.

That a package builds bit-by-bit reproducibly however is not enough to
guarantee Freedom #1.  There is another factor that is often overlooked:
opaque ascii or binary @emph{seeds} that are injected dnuring build
time.  Yes, a package may build reproduciblly from all inspectable
sourcess...but what functionality is programmed in the opaque seed?

@subsection Bootstrap Binaries
Possibly one of the most harmless, but certainly by far the biggest
binary seed that all software distributions inject are the so called
@emph{bootstrap binaries}.  Bootstrap binaries are the initial binary
seeds that are used to start building the distribution.

The GNU GuixSD operating system has a relatively small closure of
bootstrap binaries: GNU binutils, GNU gcc, GNU Libc, GNU Guile, and
``Static binaries'' (think: bash, coreutils, diffutils, findutils,
gawk, grep, gzip, make, sed, tar)

@example
$ du -schx $(readlink $(guix build bootstrap-tarballs)/*)
2.1M	/gnu/store/9623n4bq6iq5c8cwwdq99qb7d0xj93ym-binutils-static-stripped-tarball-2.28.1/binutils-static-stripped-2.28.1-x86_64-linux.tar.xz
18M	/gnu/store/437xwygmmwwpkddcyy1qvjcv4hak89pb-gcc-stripped-tarball-5.5.0/gcc-stripped-5.5.0-x86_64-linux.tar.xz
1.8M	/gnu/store/55ccx18a0d1x5y6a575jf1yr0ywizvdg-glibc-stripped-tarball-2.26.105-g0890d5379c/glibc-stripped-2.26.105-g0890d5379c-x86_64-linux.tar.xz
5.7M	/gnu/store/bqf0ajclbvnbm0a46819f30804y3ilx0-guile-static-stripped-tarball-2.2.3/guile-static-stripped-2.2.3-x86_64-linux.tar.xz
5.8M	/gnu/store/j8yzjmh9sy4gbdfwjrhw46zca43aah6x-static-binaries-tarball-0/static-binaries-0-x86_64-linux.tar.xz
33M	total
@end example

only a 33MB download that unpacks to 252BM of opaque binaries, that we
most probably have the source of, shall we review these together? ;-)

@example
$ for i in $(readlink $(guix build bootstrap-tarballs)/*);\
  do sudo tar xf $i; done
$ du -schx *
130M	bin
13M	include
54M	lib
51M	libexec
5.2M	share
252M	total
@end example

@node Full Source Bootstrap
@section  Full Source Bootstrap

There is an obvious solution: we cannot allow any binary seeds in our
software stack.  Not even in the bootstrap binaries.  Maybe that is a
bit too strong: want to have the absolute minimum of binary seeds and
all binary seeds need to be inspectable and need to be reviewed.

@subsection The Magical Self Hosting Hex Assembler

June 2016 I learnt about
@url{https://github.com/oriansj/stage0/,Stage0}.  Jeremiah Orians
created `hex0' a ~500 byte self-hosting hex assembler.  The source code
is well documented and the binary is the exact mirror of the source
code.  I was inspired: what if we could bootstrap a whole GNU
distribution from source, using only an initial 500 byte binary seed?

@subsection LISP as Maxwell's Equations of Software

As fate would have it, I stumbled upon this
@url{https://queue.acm.org/detail.cfm?id=1039523, interview with Alan
Kay}, where he shares a revelation he had when reading John McCarthy's
@url{http://www.softwarepreservation.org/projects/LISP/book/LISP%25201.5%2520Programmers%2520Manual.pdf,
LISP-1.5} manual:

@quotation
that was the big revelation to me @dots{} when I finally understood that
the half page of code on the bottom of page 13 of the Lisp 1.5 manual
was Lisp in itself.  These were “Maxwell’s Equations of Software!”  This
is the whole world of programming in a few lines that I can put my hand
over.

@author Alan Kay
@end quotation

Our starting point is @file{hex0}, a 500 byte hex assembler and we need
to somehow close the gap to building the bootstrap binaries, esp. GNU
Gcc and GNU Libc.  What better way to do that than by leveraging the
powers of LISP?

Mes is a Scheme@footnote{Scheme is a modern LISP} interpreter that will
be indirectly bootstrapped from @file{hex0} and that wields the magical
powers of LISP to close the bootstrap gap, asserting we can enjoy
software Freedom #1.

@c *********************************************************************
@node Installation
@chapter Installation

@cindex installing Mes
Mes is available for download from
@url{http://gitlab.com/janneke/mes/}.  This section describes the
software requirements of Mes, as well as how to install it and get ready
to use it.


@menu
* Regular Requirements::        Software needed to build and run Mes.
* Bootstrap Requirements::      Software needed to bootstrap Mes.
* Running the Test Suites::     Testing Mes.
@end menu

@node Regular Requirements
@section Regular Requirements

This section lists requirements when building Mes from source.  The
build procedure for Mes is the same as for other GNU software, and is
not covered here.  Please see the files @file{README} and @file{INSTALL}
in the Mes source tree for additional details.

Mes depends on the following packages:

@itemize
@item @url{http://gnu.org/software/guile/, GNU Guile}, version 2.0.13 or
later, including 2.2.x;
@item @url{http://www.gnu.org/software/make/, GNU Make}.
@item @url{https://savannah.gnu.org/projects/nyacc/, NYACC}, currently only the patched
  version 0.80.42 from @url{http://gitlab.com/janneke/nyacc/, patched
  NYACC} is known to work.
@item @url{http://gcc.gnu.org, GCC's gcc}, version 3.0.0 or later.
@end itemize

The following dependencies are optional:

@itemize
@item
Installing @url{https://github.com/oriansj/mescc-tools/, mescc-tools},
version 0.5 or later, will allow you to have MesCC assemble and link.
@end itemize

@cindex Guile, compatibility
Mes is compatible with GNU Guile, so it is possible to share the same
Scheme code between both.  Of course, Mes only supports the minimal
subset of R5RS and Guile extensions to run MesCC.

@node Bootstrap Requirements
@section Bootstrap Requirements

This section lists requirements when building Mes as a bootstrap
package.  The bootstrap build procedure for Mes is similar to building
GNU software and goes like this

@example
export PREFIX=/usr/local # for example
export MES_SEED=../mes   # for example
# optionally set some other environment variables
sh build.sh
sh check.sh
sh install.sh
@end example

See @file{build.sh} for inspiration on what environment variables to
set.

Bootstrapping Mes depends on the following packages:

@itemize
@item a POSIX-compatible shell
@item @url{https://github.com/oriansj/mescc-tools/, mescc-tools}, version 0.5 or later.
@item @url{http://gitlab.com/janneke/mes-seed/, mes-seed}, version 0.16 or later.
@end itemize

@node Running the Test Suites
@section Running the Test Suites

@cindex test suites
After a successful @command{configure} and @code{make} run, it is a good
idea to run the test suites.

@example
make check
@end example

Run Mes Scheme language semantics tests (@file{scaffold/boot}) only

@example
build-aux/check-boot.sh
@end example

Run a single Mes boot test

@example
MES_BOOT=scaffold/boot/00-zero.scm src/mes
@end example

Run a single Mes Scheme test

@example
tests/boot.test
tests/boot.test-guile
@end example

Run MesCC tests only

@example
build-aux/check-mescc.sh
@end example

Run a single MesCC test

@example
CC=gcc CC32=i686-unknown-linux-gnu-gcc MES=guile build-aux/test.sh
@end example

@node Bootstrapping
@chapter Bootstrapping

@quotation
Recipe for yogurt: Add yogurt to milk.

@author Anonymous
@end quotation

The bootstrap problem we have set out to solve is that none of our
modern software distributions, and GuixSD in particular, can be created
all from source code.  In addition to the carefully signed source code
of all the programs (the `milk') an opaque binary seed (the `yogurt') is
injected as an essential dependency.

Why would this a problem, I hear you ask?  This is how it is done, we
always did it this way, everyone does it like this!  Indeed, a popular
way of handling the bootstrapping issue is by ignoring it.

@quotation
Your compiler becoming self-hosting@dots{}a language creator's wet
dream.

@author Paul Hoogendijk
@end quotation

It seems that writing a self-hosting compiler is considered to be a
language creator's ultimate goal.  It means that their language and
compiler have become powerful enough to not depend on a pre-exising
language that possibly is---but certainly was until now---more
powerful; it feels like passing the rite to adulthood.

When you see the irony, you grasp what our bootstrapping effort means in
practice.  Creating bootstrappable software is not hard; actually most
softwares' first releases are bootstrappable.  The problem of
bootstrapping is not a technical one, it is a lack of awareness and
responsibility.

@menu
* The Mes Bootstrap Process::   How Mes will make you yogurt from pure milk.
* Invoking Mes::                Running Mes, a minimalist Guile lookalike.
* Invoking MesCC::              Running the MesCC bootstrap compiler.
@end menu

@node The Mes Bootstrap Process
@section The Mes Bootstrap Process

The Mes full source bootstrap process@footnote{TBH, the current state of
affairs demands to label this the reduced binary seed bootstrap} is
currently being developed in GuixSD@footnote{See
@file{gnu/packages/mes.scm} in the @var{wip-bootstrap} branch in Guix
git
@url{http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/mes.scm?h=wip-bootstrap}}.
In it's intiial form it is only available for x86-linux.

Currently, it goes like this:

@verbatim
mescc-tools-source + mescc-tools-seed => mescc-tools

mes-source + mescc-tools + mescc-seed => mes

tcc-source + mes + tinycc-seed => tcc

binutils-source + mes + tcc => binutils0

gcc-source + tcc + binutils0 => gcc-core

glibc-source + kernel-headers-source + binutils0 + gcc => glibc

binutils-source + binutils0 + gcc + glibc => binutils

gcc-source + binutils + gcc-core + glibc => gcc
@end verbatim

Work is ongoing to remove these binary seeds that were intentionally
injected by our own doing as temporary shortcut
@example
mescc-tools-seed, mes-seed, tinycc-seed
@end example

These additional non-bootstrapped dependencies (i.e., binary seeds) are
taken for granted

@example
BOOTSTRAP-GUILE, flex, bash,
bzip2, coreutils, diffutils, gawk, grep, gzip, make, sed, tar
@end example

Although we think these are less essential and thus less interesting
than the GNU toolchain triplet that we focussed on initially, our next
priority is to eleminate these one by one.

@node Invoking Mes
@section Invoking Mes

@cindex repl
The @command{mes} command is the Scheme interpreter whose prime
directive is to run the @command{MesCC} program.

For convenience and testing purposes, @command{mes} tries to mimic
Guile.

@example
mes @var{option}@dots{} @file{FILE}@dots{}
@end example

The @var{option}s can be among the following:

@table @code

@item -s @var{script} @var{arg}@dots{}
@cindex script mode
By default, Mes will read a file named on the command line as a script.
Any command-line arguments @var{arg}@dots{} following @var{script}
become the script's arguments; the @code{command-line} function returns
a list of strings of the form @code{(@var{script} @var{arg}@dots{})}.

Scripts are read and evaluated as Scheme source code just as the
@code{load} function would.  After loading @var{script}, Mes exits.

@item -c @var{expr} @var{arg}@dots{}
@cindex evaluate expression, command-line argument
Evaluate @var{expr} as Scheme code, and then exit.  Any command-line
arguments @var{arg}@dots{}) following @var{expr} become command-line
arguments; the @code{command-line} function returns a list of strings of
the form @code{(@var{guile} @var{arg}@dots{})}, where @var{mes} is the
path of the Mes executable.

@item -- @var{arg}@dots{}
Run interactively, prompting the user for expressions and evaluating
them.  Any command-line arguments @var{arg}@dots{} following the
@option{--} become command-line arguments for the interactive session;
the @code{command-line} function returns a list of strings of the form
@code{(@var{guile} @var{arg}@dots{})}, where @var{mes} is the path of the
Mes executable.

@item -L,--load-path=@var{directory}
Add @var{directory} to the front of Mes module load path.  The given
directories are searched in the order given on the command line and
before any directories in the @env{GUILE_LOAD_PATH} environment
variable.

@item -C,--compiled-path=@var{directory}
Accepted and ignored for Guile compatibility.

@item ---dump
dump binary program to stdout

@item -l @var{file}
Load Scheme source code from @var{file}, and continue processing the
command line.

@item -e,--main=@var{function}
Make @var{function} the @dfn{entry point} of the script.  After loading
the script file (with @option{-s}) or evaluating the expression (with
@option{-c}), apply @var{function} to a list containing the program name
and the command-line arguments---the list provided by the
@code{command-line} function.

@item -h@r{, }--help
Display help on invoking Mes, and then exit.

@item ---load
load binary program [module/mes/boot-0.32-mo]

@item -v@r{, }--version
Display the current version of Mes, and then exit.

@end table

@menu
* Environment Variables::       If the bits won't change, change their habitat.
@end menu

@node Environment Variables
@subsection Environment Variables
@cindex environment variables
@cindex shell
@cindex initialization

@c Hmm, I expected this paragraph in the Guix manual?
Here are the environment variables (see @pxref{Environment Variables,,,
guile, Guile Reference}) that affect the run-time behavior of
Mes:

@table @env
@item MES_BOOT
@vindex MES_BOOT

Set @env{MES_BOOT} to change the initial Scheme program that Mes runs.

@item MES_ARENA
@vindex MES_ARENA

The initial size of the arena @pxref{5.3,,, sicp, SICP} in cells.  Default: 20,000.

@item MES_MAX_ARENA
@vindex MES_MAX_ARENA

The maximum size of the arena in cells.  Default: 100,000,000.

@item MES_DEBUG
@vindex MES_DEBUG

@enumerate
@item
  Informational:
@itemize
@item MODULEDIR
@item included SCM modules and sources
@item result of program
@item gc stats at exit
@end itemize
@item
opened files

@item
runtime gc stats

@item
detailed info
@itemize
@item parsed, expanded program
@item list of builtins
@item list of symbol
@item opened input strings
@item gc details
@end itemize

@item
usage of opened input strings
@end enumerate


@item GUILE_LOAD_PATH
@vindex GUILE_LOAD_PATH
This variable may be used to augment the path that is searched for
Scheme files when loading.  Its value should be a colon-separated list
of directories.  If it contains the special path component @code{...}
(ellipsis), then the default path is put in place of the ellipsis,
otherwise the default path is placed at the end.  The result is stored
in @code{%load-path}.

Mes uses @var{@strong{GUILE}_LOAD_PATH} for compatibility with Guile.

@end table

@node Invoking MesCC
@section Invoking MesCC

@example
mescc @var{option}@dots{} @file{FILE}@dots{}
@end example

The @var{option}s can be among the following:

@table @code

@item -c
@cindex compile
preprocess, compile and assemble only; do not link

@item -D @var{DEFINE}[=@var{VALUE}]
@cindex define DEFINE [VALUE=1]

@item -E
preprocess only; do not compile, assemble or link

@item -g
add @command{blood-elf} debug info

This enables GDB setting breakpoints on function names, and to have the
GDB backtrace command to show the function call stack.

@item -h, --help
display this help and exit

@item -I DIR
append DIR to include path

@item -L DIR
append DIR to library path

@item -l LIBNAME
link with LIBNAME

@item -o FILE
write output to FILE

@item -S
preprocess and compile only; do not assemble or link

@item -v, --version
display version and exit

@item -w,--write=TYPE
dump Nyacc AST using TYPE @{pretty-print,write@}

@end table

@menu
* MesCC Environment Variables::  There's no NIX like POSIX.
@end menu

@node MesCC Environment Variables
@subsection MesCC Environment Variables

@table @env
@item MES
@vindex MES

Setting @env{MES} to a mes-compatible Scheme will run MesCC using that
@example
MES=guile mescc -c scaffold/main.c
@end example

See, now Guile has become compatible with Mes, instead of the other way
around ;-)

@item C_INCLUDE_PATH
@vindex C_INCLUDE_PATH

@item LIBRARY_PATH
@vindex LIBRARY_PATH

@item NYACC_DEBUG
@vindex NYACC_DEBUG

Setting @env{NYACC_DEBUG} makes nyacc print names of function
during the parsing phase.

@end table


@c *********************************************************************
@node Contributing
@chapter Contributing

@menu
* Building from Git::           The latest and greatest.
* Running Mes From the Source Tree::  Hacker tricks.
* The Perfect Setup::           The right tools.
* Coding Style::                Hygiene of the contributor.
* Submitting Patches::          Share your work.
@end menu

@node Building from Git
@section Building from Git

If you want to hack Mes itself, it is recommended to use the latest
version from the Git repository:

@example
git clone https://gitlab.com/janneke/mes.git
@end example

The easiest way to set up a development environment for Mes is, of
course, by using Guix!  The following command starts a new shell where
all the dependencies and appropriate environment variables are set up to
hack on Mes:

@example
guix environment -l guix.scm
@end example

Finally, you have to invoke @code{make check} to run tests
(@pxref{Running the Test Suites}).  If anything fails, take a look at
installation instructions (@pxref{Installation}) or send a message to
@email{janneke@@gnu.org, janneke} or to the @email{guix-devel@@gnu.org}
mailing list.

@node Running Mes From the Source Tree
@section Running Mes From the Source Tree

Running Mes from the source tree is supported out of the box.  This has
been accomplished by using some magic and heuristics.  These should be
removed and if necessary replaced by a @file{./pre-inst-env} trick.

@node The Perfect Setup
@section The Perfect Setup

The Perfect Setup to hack on Mes is basically the perfect setup used
for Guile hacking (@pxref{Using Guile in Emacs,,, guile, Guile Reference
Manual}).  First, you need more than an editor, you need
@url{http://www.gnu.org/software/emacs, Emacs}, empowered by the
wonderful @url{http://nongnu.org/geiser/, Geiser}.

Geiser allows for interactive and incremental development from within
Emacs: code compilation and evaluation from within buffers, access to
on-line documentation (docstrings), context-sensitive completion,
@kbd{M-.} to jump to an object definition, a REPL to try out your code,
and more (@pxref{Introduction,,, geiser, Geiser User Manual}).

@node Coding Style
@section Coding Style

In general our code follows the GNU Coding Standards (@pxref{Top,,,
standards, GNU Coding Standards}).  However, they do not say much about
Scheme, so here are some additional rules.

@subsection Programming Paradigm

Scheme code in Mes is written in a purely functional style.

@subsection Formatting Code

@cindex formatting code
@cindex coding style
When writing Scheme code, we follow common wisdom among Scheme
programmers.  In general, we follow the
@url{http://mumble.net/~campbell/scheme/style.txt, Riastradh's Lisp
Style Rules}.  This document happens to describe the conventions mostly
used in Guile’s code too.  It is very thoughtful and well written, so
please do read it.

@cindex indentation, of code
@cindex formatting, of code
If you do not use Emacs, please make sure to let your editor knows these
rules.

Additionally, in Mes we prefer to format @code{if} statements like this
@example
(if foo? trivial-then
    (let ((bar (the-longer @dots{})))
      more-complicated
      @dots{}
      else))
@end example

@node Submitting Patches
@section Submitting Patches

Development is done using the Git distributed version control system.
Thus, access to the repository is not strictly necessary.  We welcome
contributions in the form of patches as produced by @code{git
format-patch} sent to @email{janneke@@gnu.org, janneke} or to the
@email{guix-devel@@gnu.org} mailing list.

Please write commit logs in the ChangeLog format (@pxref{Change Logs,,,
standards, GNU Coding Standards}); you can check the commit history for
examples.

@subsection Reporting Bugs

Encountering a problem or bug can be very frustrating for you as a user
or potential contributor.  For us as Mes maintainers, the preferred bug
report includes a beautiful and tested patch that we can integrate
without any effort.

However, please don't let our preference stop you from reporting a bug.
There's one thing @emph{much} worse for us than getting a bug report
without a patch: Reading a complaint or rant online about your pain and
how our work sucks, without having heard directly what you experienced.

So if you report a problem, will it be fixed?  And @strong{when}?  The
most honest answer is: It depends.  Let's curry that informationless
honesty with a more helpful and more blunt reminder of a mantra of Free
Software:

@quotation
When@dots{}?

@dots{}sooner if you help.

@author Eric Raymond
@end quotation

@cindex contact, irc, mailing list
@cindex bug, bug report, reporting a bug
Join us on @code{#bootstrappable} on the Freenode IRC network or on
@file{guix-devel@@gnu.org} to share your experience---good or bad.


@c *********************************************************************
@node Acknowledgments
@chapter Acknowledgments

We would like to thank the following people for their help: Jeremiah
Orians, pdewacht, rain1, Ricardo Wurmus, Rutger van Beusekom.

We also thank Ludovic Courtès for creating GuixSD and making the
bootstrap problem so painfully visible, John McCarthy for creating
LISP-1.5 and Alan Kay for their observation that Page 13
@url{https://queue.acm.org/detail.cfm?id=1039523, Page 13}.

@c *********************************************************************
@node GNU Free Documentation License
@appendix GNU Free Documentation License
@cindex license, GNU Free Documentation License
@include fdl-1.3.texi

@c *********************************************************************
@node Concept Index
@unnumbered Concept Index
@printindex cp

@node Programming Index
@unnumbered Programming Index
@syncodeindex tp fn
@syncodeindex vr fn
@printindex fn

@bye

@c Local Variables:
@c ispell-local-dictionary: "american";
@c End: