path: root/HACKING

-*-text-*-
Guile Hacking Guide
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2008 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
   copyright notice and permission notice are preserved,
   and that the distributor grants the recipient permission
   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the version you find may be out of date; a CVS checkout is recommended: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 CVS, 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 listed below, correctly installed.
i.e., they must be found in the current PATH and not shadowed or
otherwise broken by files left behind from other versions.

"up-to-date" means the latest released versions at the time that Guile
was obtained from CVS.  Sometimes older or newer versions will work.
(See below for versions to avoid.)

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

In case of problems, it may be worth getting a fresh copy of Guile
from CVS: synchronisation problems have been known to occur
occasionally.

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 1.5.26 (or
	later) is needed for correct AIX support.

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.

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.

- (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.  The best
place to post it is guile-devel@gnu.org.  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.

- 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).

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.


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

- Before contributing larger amounts of code to Guile, please read the
documents in `guile-core/devel/policy' in the CVS source tree.

- 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.  :)

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.

- 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 do 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.

- 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_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 log entry.

- There's no need to keep a change log for a ChangeLog file.  For any
other kind of file (including documentation, since our documentation
is indeed precisely engineered -- we surpass GNU standards here), add
an appropriate ChangeLog entry when you change it.  Simple!

- 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.


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.

- 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, and others


Patches ===========================================================

This one makes cvs-1.10 consider the file $CVSDOTIGNORE instead of
.cvsignore when that environment variable is set.

=== patch start ===
diff -r -u cvs-1.10/src/cvs.h cvs-1.10.ignore-hack/src/cvs.h
--- cvs-1.10/src/cvs.h	Mon Jul 27 04:54:11 1998
+++ cvs-1.10.ignore-hack/src/cvs.h	Sun Jan 23 12:58:09 2000
@@ -516,7 +516,7 @@

 extern int ign_name PROTO ((char *name));
 void ign_add PROTO((char *ign, int hold));
-void ign_add_file PROTO((char *file, int hold));
+int ign_add_file PROTO((char *file, int hold));
 void ign_setup PROTO((void));
 void ign_dir_add PROTO((char *name));
 int ignore_directory PROTO((char *name));
diff -r -u cvs-1.10/src/ignore.c cvs-1.10.ignore-hack/src/ignore.c
--- cvs-1.10/src/ignore.c	Mon Sep  8 01:04:15 1997
+++ cvs-1.10.ignore-hack/src/ignore.c	Sun Jan 23 12:57:50 2000
@@ -99,9 +99,9 @@
 /*
  * Open a file and read lines, feeding each line to a line parser. Arrange
  * for keeping a temporary list of wildcards at the end, if the "hold"
- * argument is set.
+ * argument is set.  Return true when the file exists and has been handled.
  */
-void
+int
 ign_add_file (file, hold)
     char *file;
     int hold;
@@ -149,8 +149,8 @@
     if (fp == NULL)
     {
 	if (! existence_error (errno))
-	    error (0, errno, "cannot open %s", file);
-	return;
+	  error (0, errno, "cannot open %s", file);
+	return 0;
     }
     while (getline (&line, &line_allocated, fp) >= 0)
 	ign_add (line, hold);
@@ -159,6 +159,7 @@
     if (fclose (fp) < 0)
 	error (0, errno, "cannot close %s", file);
     free (line);
+    return 1;
 }

 /* Parse a line of space-separated wildcards and add them to the list. */
@@ -375,6 +376,7 @@
     struct stat sb;
     char *file;
     char *xdir;
+    char *cvsdotignore;

     /* Set SUBDIRS if we have subdirectory information in ENTRIES.  */
     if (entries == NULL)
@@ -397,7 +399,10 @@
     if (dirp == NULL)
 	return;

-    ign_add_file (CVSDOTIGNORE, 1);
+    cvsdotignore = getenv("CVSDOTIGNORE");
+    if (cvsdotignore == NULL || !ign_add_file (cvsdotignore, 1))
+      ign_add_file (CVSDOTIGNORE, 1);
+
     wrap_add_file (CVSDOTWRAPPER, 1);

     while ((dp = readdir (dirp)) != NULL)
=== patch end ===

This one is for pcl-cvs-2.9.2, so that `i' adds to the local
.cvsignore file.

=== patch start ===
--- pcl-cvs.el~ Mon Nov  1 12:33:46 1999
+++ pcl-cvs.el  Tue Jan 25 21:46:27 2000
@@ -1177,7 +1177,10 @@
   "Append the file in FILEINFO to the .cvsignore file.
 Can only be used in the *cvs* buffer."
   (save-window-excursion
-    (set-buffer (find-file-noselect (expand-file-name ".cvsignore" dir)))
+    (set-buffer (find-file-noselect
+                (expand-file-name (or (getenv "CVSDOTIGNORE")
+                                      ".cvsignore")
+                                  dir)))
     (goto-char (point-max))
     (unless (zerop (current-column)) (insert "\n"))
     (insert str "\n")
=== patch end ===