guile/HACKING

-*-text-*-
Guile Hacking Guide
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2008, 2012,
 2015 Free software Foundation, Inc.

   Permission is granted to anyone to make or distribute verbatim copies
   of this document as received, in any medium, provided that the
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   for further redistribution as permitted by this notice.

   Permission is granted to distribute modified versions
   of this document, or of portions of it,
   under the above conditions, provided also that they
   carry prominent notices stating who last changed them,
   and that any new or changed statements about the activities
   of the Free Software Foundation are approved by the Foundation.


What to Hack =========================================================

You can hack whatever you want, thank GNU.

However, to see what others have indicated as their interest (and avoid
potential wasteful duplication of effort), see file TODO.  Note that
the version you find may be out of date; a CVS checkout is recommended:
see below for details (see also the files ANON-CVS and SNAPSHOTS).

It's also a good idea to join the guile-devel@gnu.org mailing list.
See http://www.gnu.org/software/guile/mail/mail.html for more info.


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

When Guile is obtained from Git, a few extra steps must be taken
before the usual configure, make, make install.  You will need to have
up-to-date versions of the tools as listed below, correctly installed.

Sometimes older or newer versions will work.  (See below for versions
to avoid.)

Then you must run the autogen.sh script, as described below.

The same procedure can be used to regenerate the files in released
versions of Guile.  In that case the headers of the original generated
files (e.g., configure, Makefile.in, ltmain.sh) can be used to
identify which tool versions may be required.

Autoconf --- 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 --- 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"

libtool --- 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".  Version 2.2 (or
	later) is recommended (for correct AIX support, and correct
	interaction with the Gnulib module for using libunistring).

gettext --- a system for rigging a program so that it can output its
        messages in the local tongue.  Guile presently only exports
        the gettext functionality to Scheme, it does not use it
        itself.

flex --- a scanner generator.  It's probably not essential to have the
        latest version; Flex 2.5.37 is known to work.

One false move and you will be lost in a little maze of automatically
generated files, all different.

Here is the authoritative list of tool/version/platform tuples that
have been known to cause problems, and a short description of the problem.

- automake 1.4 adds extraneous rules to the top-level Makefile if
  you specify specific Makefiles to rebuild on the command line.

- automake 1.4-p4 (debian "1:1.4-p4-1.1") all platforms
  automake "include" facility does not recognize filenames w/ "-".

- libtool 1.4 uses acconfig.h, which is deprecated by newest autoconf
  (which constructs the equivalent through 3rd arg of AC_DEFINE forms).

- autoreconf from autoconf prior to 2.59 will run gettextize, which
  will mess up the Guile tree.

- libtool 1.5.26 does not know that it should remove the -R options
  that the Gnulib libunistring and havelib modules generate (because
  gcc doesn't actually support -R).

- (add here.)


Sample GDB Initialization File=========================================

Here is a sample .gdbinit posted by Bill Schottstaedt (modified to
use `set' instead of `call' in some places):

  define gp
  set gdb_print($arg0)
  print gdb_output
  end
  document gp
  Executes (object->string arg)
  end

  define ge
  call gdb_read($arg0)
  call gdb_eval(gdb_result)
  set gdb_print(gdb_result)
  print gdb_output
  end
  document ge
  Executes (print (eval (read arg))): ge "(+ 1 2)" => 3
  end

  define gh
  call g_help(scm_str2symbol($arg0), 20)
  set gdb_print($1)
  print gdb_output
  end
  document gh
  Prints help string for arg: gh "enved-target"
  end

Bill further writes:

  so in gdb if you see something useless like:

  #32 0x081ae8f4 in scm_primitive_load (filename=1112137128) at load.c:129

  You can get the file name with gp:

  (gdb) gp 1112137128
  $1 = 0x40853fac "\"/home/bil/test/share/guile/1.5.0/ice-9/session.scm\""


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.  Post your
patch to guile-devel@gnu.org.

- We prefer patches generated using 'git format-patch'.

- Provide a description in the commit message, like so:

  1-line description of change

  More extensive discussion of your change.  Document why you are
  changing things.

  * filename (function name): file specific change comments.

- For proper credit, also make sure you update the AUTHORS file
(for new files for which you've assigned copyright to the FSF), or
the THANKS file (for everything else).


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

To make sure of this, you can use the --enable-error-on-warning option
to configure.  This option will make GCC fail if it hits a warning.

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.  :)

- 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.

- The normal way of removing a function, macro or variable is to mark
it as "deprecated", keep it for a while, and remove it in a later
release.  If a function or macro is marked as "deprecated" it
indicates that people shouldn't use it in new programs, and should try
to remove it in old.  Make sure that an alternative exists unless it
is our purpose to remove functionality.  Don't deprecate definitions
if it is unclear when they will be removed.  (This is to ensure that a
valid way of implementing some functionality always exists.)

When deprecating a definition, always follow this procedure:

1. Mark the definition using

   #if (SCM_DEBUG_DEPRECATED == 0)
   ...
   #endif

   or, for Scheme code, wrap it using

   (begin-deprecated
      ...)

2. Make the deprecated code issue a warning when it is used, by using
   scm_c_issue_deprecation_warning (in C) or issue-deprecation-warning
   (in Scheme).

3. Write a comment at the definition explaining how a programmer can
   manage without the deprecated definition.

4. Add an entry that the definition has been deprecated in NEWS and
   explain what to do instead.

5. In file TODO, there is a list of releases with reminders about what
   to do at each release.  Add a reminder about the removal of the
   deprecated defintion at the appropriate release.

- Write commit messages for functions written in C using the
functions' C names, and write entries for functions written in Scheme
using the functions' Scheme names.  For example,

  * foo.c: Moved scm_procedure_documentation from eval.c.

is preferred over

  * foo.c: Moved procedure-documentation from eval.c.

Changes like adding this line are special:

    SCM_PROC (s_map_in_order, "map-in-order", 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 commit message.

- 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.

Once you accept a contribution, be sure to keep the files AUTHORS and
THANKS uptodate.

- 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.

- When you get bug reports or patches from people, be sure to list
them in THANKS.

- Do not introduce trailing whitespace (and feel free to clean it up
opportunistically, that is, if doing so is part of some other change).
The goal is to reduce (and over time, eliminate) spurious diffs.

For Emacs users:
  (add-hook 'before-save-hook 'delete-trailing-whitespace)

Naming conventions =================================================

We use certain naming conventions to structure the considerable number
of global identifiers.  All identifiers should be either all lower
case or all upper case.  Syllables are separated by underscores `_'.
All non-static identifiers should start with scm_ or SCM_.  Then might
follow zero or more syllables giving the category of the identifier.
The currently used category identifiers are

    t   - type name

    c,C - something with a interface suited for C use.  This is used
          to name functions that behave like Scheme primitives but
          have a more C friendly calling convention.

    i,I - internal to libguile.  It is global, but not considered part
          of the libguile API.

    f   - a SCM variable pointing to a Scheme function object.

    F   - a bit mask for a flag.

    m   - a macro transformer procedure

    n,N - a count of something

    s   - a constant C string

    k   - a SCM variable pointing to a keyword.

  sym   - a SCM variable pointing to a symbol.

  var   - a SCM variable pointing to a variable object.

The follwing syllables also have a technical meaning:

  str   - this denotes a zero terminated C string

  mem   - a C string with an explicit count


See also the file `devel/names.text'.


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.


Jim Blandy, and others