Re: more m4sugar tweaks

[Eric Blake]

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According to Ralf Wildenhues on 8/22/2008 8:02 AM:
>> This meant the user could modify the definition of variable
>> to skip or replay iterations, potentially even entering an infinite loop.
>> ~  The new implementation ignores user changes to variable, always
>> performing as many iterations as was determined up front.
> 
> That's ok.  However, do we provide for a method that allows a for-like
> loop which allows to mess with the iteration variable while looping?

Not currently; the user would have to write the recursion themselves.

> Asking because that may allow for a "break"-like construct.  I'm not
> asking you to implement this if we don't have it yet (a TODO item would
> be fine), but if we do, hinting at it in the manual would be nice.  It
> is not a problem if this method is slower than m4_for.

I'm adding this as a TODO item (it doesn't bother me enough to try
implementing it now).  Other thoughts - maybe provide m4_break, which
normally is an error, but when executed inside this new loop macro, will
gracefully stop iteration.  Or provide something like m4_while(TEST, EXPR)
which evaluates EXPR repeatedly until TEST expands to the empty string
(hopefully EXPR modifies whatever TEST will expand to).

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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>From 0b8af134157753edec45bb9f78795596b1fcd07a Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Fri, 22 Aug 2008 08:31:03 -0600
Subject: [PATCH] * TODO: Add an item for additional m4sugar looping constructs.

Suggested by Ralf Wildenhues.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog |    3 +++
 TODO      |   13 +++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 6a642cd..9a90bde 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2008-08-22  Eric Blake  <address@hidden>
 
+       * TODO: Add an item for additional m4sugar looping constructs.
+       Suggested by Ralf Wildenhues.
+
        Add reminder to keep dual implementations in sync.
        * lib/m4sugar/m4sugar.m4: Add comments.
        * lib/m4sugar/foreach.m4: Likewise.
diff --git a/TODO b/TODO
index 368268c..f85ba54 100644
--- a/TODO
+++ b/TODO
@@ -228,6 +228,15 @@ this for translators.
 F**k!  --trace FOO does not catch indir([FOO], $@)!
 Fixed in M4 1.6, but we can't rely on it yet.
 
+** m4 loops
+As of 2.63, m4_for has a fixed iteration count for speed in the common
+usage case.  But it used to allow the user to alter iteration count by
+reassigning the iterator, allowing a break-like functionality (or even
+infloops).  Does this need a new (but maybe slower) macro?  Should we
+also provide something like m4_while([TEST], [EXPR])?  Maybe an
+m4_break() that works inside a looping construct?
+http://lists.gnu.org/archive/html/autoconf-patches/2008-08/msg00121.html
+
 * Autoconf 3
 
 ** Cache name spaces.
@@ -246,7 +255,7 @@ should depend upon the current language.
 I think one sad decision in Autoconf was to use white space separated
 lists for some arguments.  For instance AC_CHECK_FUNCS(foo bar).  I
 tend to think that, even if it is not as nice, we should use m4 lists,
-i.e., AC_CHECK_FUNCS((foo, bar)) in this case.  This would ease
+i.e., AC_CHECK_FUNCS([foo, bar]) in this case.  This would ease
 specializing loops, and more importantly, make them much more robust.
 
 A typical example of things that can be performed if we use m4 lists
@@ -255,7 +264,7 @@ a space in their names, eg, structures.
 
 With the current scheme it would be extremely difficult to loop over
 AC_CHECK_STRUCTS(struct foo struct bar), while it natural and well
-defined for m4 lists: AC_CHECK_STRUCTS((struct foo, struct bar)).
+defined for m4 lists: AC_CHECK_STRUCTS([struct foo, struct bar]).
 
 I know that makes a huge difference in syntax, but a major release
 should be ready to settle a new world.  We *can* provide helping tools
-- 
1.6.0