guile/HACKING

Hacking It Yourself ==================================================

As distributed, Guile needs only an ANSI C compiler and a Unix system
to compile.  However, Guile's makefiles, configuration scripts, and a
few other files are automatically generated, not written by hand.  If
you want to make changes to the system (which we encourage!) you will
find it helpful to have the tools we use to develop Guile.  They
are the following:

Autoconf 2.13 --- a system for automatically generating `configure'
	scripts from templates which list the non-portable features a
	program would like to use.  Available in
	"ftp://ftp.gnu.org/pub/gnu/autoconf"

Automake 1.4 --- a system for automatically generating Makefiles that
	conform to the (rather Byzantine) GNU coding standards.  The
	nice thing is that it takes care of hairy targets like 'make
	dist' and 'make distclean', and automatically generates
	Makefile dependencies.  Automake is available in
	"ftp://ftp.gnu.org/pub/gnu/automake"

	Before using automake, you may need to copy `threads.m4' and
	`guile.m4' from the top directory of the Guile core disty to
	`/usr/local/share/aclocal.

libtool 1.3.4 --- a system for managing the zillion hairy options needed
	on various systems to produce shared libraries.  Available in
	"ftp://ftp.gnu.org/pub/gnu/libtool"

You are lost in a little maze of automatically generated files, all
different.
> 


Contributing Your Changes ============================================

- If you have put together a change that meets the coding standards
described below, we encourage you to submit it to Guile.  The best
place to post it is guile@sourceware.cygnus.com.  Please don't send it
directly to me; I often don't have time to look things over.  If you
have tested your change, then you don't need to be shy.

- Please submit patches using either context or unified diffs (diff -c
or diff -u).  Don't include a patch for ChangeLog; such patches don't
apply cleanly, since we've probably changed the top of ChangeLog too.
Instead, provide the unaltered text at the top of your patch.

Please don't include patches for generated files like configure,
aclocal.m4, or any Makefile.in.  Such patches are often large, and
we're just going to regenerate those files anyway.


CVS conventions ======================================================

- We use CVS to manage the Guile sources.  The repository lives on
egcs.cygnus.com, in /cvs/guile; you will need an
account on that machine to access the repository.  Also, for security
reasons, egcs presently only supports CVS connections via the SSH
protocol, so you must first install the SSH client.  Then, you should
set your CVS_RSH environment variable to ssh, and use the following as
your CVS root:

	:ext:USER@egcs.cygnus.com:/cvs/guile

Either set your CVSROOT environment variable to that, or give it as
the value of the global -d option to CVS when you check out a working
directory.

For more information on SSH, see http://www.cs.hut.fi/ssh.

The Guile sources live in several modules:

  - guile-core --- the interpreter, QuickThreads, and ice-9
  - guile-doc --- documentation in progress.  When complete, this will
	be incorporated into guile-core.
  - guile-oops --- The Guile Object-Oriented Programming System (talk to mdj)
  - guile-tcltk --- the Guile/Tk interface
  - guile-tk --- the new Guile/Tk interface, based on STk's modified Tk
  - guile-rgx-ctax --- the Guile/Rx interface, and the ctax implementation
  - guile-scsh --- the port of SCSH to guile, talk to Gary Houston
  - guile-www --- A Guile module for making HTTP requests.

There is a mailing list for CVS commit messages; see README for details.

- We check Makefile.am and configure.in files into CVS, but the
"autogen.sh" script must be run from the top-level to generate the
actual "configure" script that then must be run to create the various
Makefile-s to build guile. The general rule is that you should be able
to check out a working directory of Guile from CVS, and then type
"./autogen.sh", then "configure", and finally "make".

- (Automake 1.4 only) Be sure to run automake at the top of the tree
with no arguments.  Do not use `automake Makefile' to regenerate
specific Makefile.in files, and do not trust the Makefile rules to
rebuild them when they are out of date.  Automake 1.4 will add
extraneous rules to the top-level Makefile if you specify specific
Makefiles to rebuild on the command line.  Running the command
`autoreconf --force' should take care of everything correctly.

- Make sure your changes compile and work, at least on your own
machine, before checking them into the main branch of the Guile
repository.  If you really need to check in untested changes, make a
branch.

- Include each log entry in both the ChangeLog and in the CVS logs.
If you're using Emacs, the pcl-cvs interface to CVS has features to
make this easier; it checks the ChangeLog, and generates good default
CVS log entries from that.


Coding standards =====================================================

- As for any part of Project GNU, changes to Guile should follow the
GNU coding standards.  The standards are available via anonymous FTP
from prep.ai.mit.edu, as /pub/gnu/standards/standards.texi and
make-stds.texi.

- The Guile tree should compile without warnings under the following
GCC switches, which are the default in the current configure script:
    -O2 -Wall -Wpointer-arith -Wmissing-prototypes
The only warnings which can be tolerated are those about variables
being clobbered by longjmp/vfork in eval.c.  The variables in question
are critical to the interpreter's performance; as far as I can tell,
it is difficult/annoying to avoid these warnings without slowing the
system down substantially.  (If you can figure out a good fix, I'd be happy to see it.)

Note that the warnings generated vary from one version of GCC to the
next, and from one architecture to the next (apparently).  To provide
a concrete common standard, Guile should compile without warnings from
GCC 2.7.2.3 in a Red Hat 5.2 i386 Linux machine.  Furthermore, each
developer should pursue any additional warnings noted by on their
compiler.  This means that people using more stringent compilers will
have more work to do, and assures that everyone won't switch to the
most lenient compiler they can find.  :)

Note also that EGCS (as of November 3 1998) doesn't handle the
`noreturn' attribute properly, so it doesn't understand that functions
like scm_error won't return.  This may lead to some silly warnings
about uninitialized variables.  You should look into these warnings to
make sure they are indeed spurious, but you needn't correct warnings
caused by this EGCS bug.

- If you add code which uses functions or other features that are not
entirely portable, please make sure the rest of Guile will still
function properly on systems where they are missing.  This usually
entails adding a test to configure.in, and then adding #ifdefs to your
code to disable it if the system's features are missing.

- When you make a user-visible change (i.e. one that should be
documented, and appear in NEWS, put an asterisk in column zero of the
start of the ChangeLog entry, like so:

Sat Aug  3 01:27:14 1996  Gary Houston  <ghouston@actrix.gen.nz>

*	* fports.c (scm_open_file): don't return #f, throw error.

When you've written a NEWS entry and updated the documentation, go
ahead and remove the asterisk.  I will use the asterisks to find and
document changes that haven't been dealt with before a release.

- Please write log entries for functions written in C under the
functions' C names, and write log entries for functions written in
Scheme under the functions' Scheme names.  Please don't do this:

	* procs.c, procs.h (procedure-documentation): Moved from eval.c.

Entries like this make it harder to search the ChangeLogs, because you
can never tell which name the entry will refer to.  Instead, write this:

	* procs.c, procs.h (scm_procedure_documentation): Moved from eval.c.

Changes like adding this line are special:

    SCM_PROC (s_serial_map, "serial-map", 2, 0, 1, scm_map);

Since the change here is about the name itself --- we're adding a new
alias for scm_map that guarantees the order in which we process list
elements, but we're not changing scm_map at all --- it's appropriate
to use the Scheme name in the log entry.

- There's no need to keep a change log for documentation files.  This
is because documentation is not susceptible to bugs that are hard to
fix.  Documentation does not consist of parts that must interact in a
precisely engineered fashion; to correct an error, you need not know
the history of the erroneous passage.  (This is copied from the GNU
coding standards.)

- Make sure you have papers from people before integrating their
changes or contributions.  This is very frustrating, but very
important to do right.  From maintain.texi, "Information for
Maintainers of GNU Software":

    When incorporating changes from other people, make sure to follow the
    correct procedures.  Doing this ensures that the FSF has the legal
    right to distribute and defend GNU software.

    For the sake of registering the copyright on later versions ofthe
    software you need to keep track of each person who makes significant
    changes.  A change of ten lines or so, or a few such changes, in a
    large program is not significant.

    *Before* incorporating significant changes, make sure that the person
    has signed copyright papers, and that the Free Software Foundation has
    received them.

If you receive contributions you want to use from someone, let me know
and I'll take care of the administrivia.  Put the contributions aside
until we have the necessary papers.

- When you make substantial changes to a file, add the current year to
the list of years in the copyright notice at the top of the file.


Helpful hints ========================================================

- [From Mikael Djurfeldt] When working on the Guile internals, it is
quite often practical to implement a scheme-level procedure which
helps you examine the feature you're working on.

Examples of such procedures are: pt-size, debug-hand and
current-pstate.

I've now put #ifdef GUILE_DEBUG around all such procedures, so that
they are not compiled into the "normal" Guile library.  Please do the
same when you add new procedures/C functions for debugging purpose.

You can define the GUILE_DEBUG flag by passing --enable-guile-debug to
the configure script.

- You'll see uses of the macro SCM_P scattered throughout the code;
those are vestiges of a time when Guile was meant to compile on
pre-ANSI compilers.  Guile now requires ANSI C, so when you write new
functions, feel free to use ANSI declarations, and please provide
prototypes for everything.  You don't need to use SCM_P in new code.


Jim Blandy