allow nameless m4_for iteration

[Eric Blake]

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Borrowing an idea from the m4 manual:

m4_for(,1,3,,-) should result in ---, not an error.

2007-09-30  Eric Blake  <address@hidden>

        Allow nameless iteration.
        * lib/m4sugar/m4sugar.m4 (m4_for, _m4_for): Access variable
        indirectly.
        * tests/m4sugar.at (myvar): Test this.

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

Eric Blake             address@hidden
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>From 615300a1d5e4a7bb89df2d40b8acf2ede38142d0 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Sun, 30 Sep 2007 06:27:46 -0600
Subject: [PATCH] Allow nameless iteration.

* lib/m4sugar/m4sugar.m4 (m4_for, _m4_for): Access variable
indirectly.
* tests/m4sugar.at (myvar): Test this.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog              |    7 +++++++
 lib/m4sugar/m4sugar.m4 |   17 +++++++++++------
 tests/m4sugar.at       |    4 ++++
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 69d2053..cfe81ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-09-30  Eric Blake  <address@hidden>
+
+       Allow nameless iteration.
+       * lib/m4sugar/m4sugar.m4 (m4_for, _m4_for): Access variable
+       indirectly.
+       * tests/m4sugar.at (myvar): Test this.
+
 2007-09-29  Eric Blake  <address@hidden>
 
        Speed optimization: avoid m4 regex when other algorithms work.
diff --git a/lib/m4sugar/m4sugar.m4 b/lib/m4sugar/m4sugar.m4
index 8fea736..bd3fb17 100644
--- a/lib/m4sugar/m4sugar.m4
+++ b/lib/m4sugar/m4sugar.m4
@@ -580,16 +580,21 @@ m4_builtin([undefine], $@)])
 # --------------------------------------------------------
 # Expand EXPRESSION defining VARIABLE to FROM, FROM + 1, ..., TO.
 # Both limits are included, and bounds are checked for consistency.
+# The algorithm is robust to indirect VARIABLE names.
 m4_define([m4_for],
 [m4_pushdef([$1], m4_eval([$2]))dnl
-m4_if(m4_eval(([$3]) > $1), 1,
+m4_if(m4_eval(([$3]) > m4_defn([$1])), 1,
 [m4_pushdef([_m4_step], m4_eval(m4_default([$4], 1)))dnl
 m4_assert(_m4_step > 0)dnl
-_m4_for([$1], m4_eval((([$3]) - $1) / _m4_step * _m4_step + $1), _m4_step, 
[$5])],
-      m4_eval(([$3]) < $1), 1,
+_m4_for([$1], m4_eval((([$3]) - m4_defn([$1]))
+                     / _m4_step * _m4_step + m4_defn([$1])),
+       _m4_step, [$5])],
+      m4_eval(([$3]) < m4_defn([$1])), 1,
 [m4_pushdef([_m4_step], m4_eval(m4_default([$4], -1)))dnl
 m4_assert(_m4_step < 0)dnl
-_m4_for([$1], m4_eval(($1 - ([$3])) / -(_m4_step) * _m4_step + $1), _m4_step, 
[$5])],
+_m4_for([$1], m4_eval((m4_defn([$1]) - ([$3]))
+                     / -(_m4_step) * _m4_step + m4_defn([$1])),
+       _m4_step, [$5])],
       [m4_pushdef(_m4_step,[])dnl
 $5])[]dnl
 m4_popdef([_m4_step])dnl
@@ -601,8 +606,8 @@ m4_popdef([$1])])
 # Core of the loop, no consistency checks, all arguments are plain numbers.
 m4_define([_m4_for],
 [$4[]dnl
-m4_if($1, [$2], [],
-      [m4_define([$1], m4_eval($1+[$3]))_m4_for([$1], [$2], [$3], [$4])])])
+m4_if(m4_defn([$1]), [$2], [],
+      [m4_define([$1], m4_eval(m4_defn([$1])+[$3]))$0($@)])])
 
 
 # Implementing `foreach' loops in m4 is much more tricky than it may
diff --git a/tests/m4sugar.at b/tests/m4sugar.at
index 6f3da58..5aff0c9 100644
--- a/tests/m4sugar.at
+++ b/tests/m4sugar.at
@@ -281,6 +281,9 @@ m4_for([myvar], -2+8, 3-5, , [ myvar])
 m4_for([myvar], 8, 16, 3 * 2, [ myvar])
 m4_for([myvar], 8, 16, -3 * -2, [ myvar])
 m4_for([myvar], [2<<2], [2<<3], [-3 * (-2)], [ myvar])
+dnl Make sure we can do nameless iteration
+m4_for(, 1, 10, , -)
+dnl foreach tests
 m4_foreach([myvar], [[a], [b, c], [d], [e
 ],[f]], [ myvar|])
 m4_foreach_w([myvar], [a  b c, d,e f
@@ -313,6 +316,7 @@ myvar
  8 14
  8 14
  8 14
+----------
  a| b, c| d| e
 | f|
  a| b| c,| d,e| f| g|
-- 
1.5.3.2