+2008-08-21 Eric Blake <ebb9@byu.net>
+
+ Avoid extra side effects in m4sugar list expansion.
+ * lib/m4sugar/m4sugar.m4 (m4_mapall_sep, m4_list_cmp): Wrap
+ around...
+ (_m4_mapall_sep, _m4_list_cmp_raw): ...new helpers, to avoid
+ duplicate side effects.
+ (m4_version_compare): Adjust caller.
+ * lib/m4sugar/foreach.m4 (m4_list_cmp): Rename...
+ (_m4_list_cmp_raw): ...to match m4sugar.
+ * doc/autoconf.texi (Looping constructs): Document the behavior of
+ side effects.
+ * tests/m4sugar.at (M4 loops, m4@&t@_map, m4@&t@_version_compare):
+ Ensure only one side effect.
+ (recursion): Fix test typo.
+ Reported by Ralf Wildenhues.
+
2008-08-21 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
* TODO: Add item for compiler default flags.
not likely to be macro names, as in @samp{[fputc_unlocked,
fgetc_unlocked]}.
+Although not generally recommended, it is possible for quoted lists to
+have side effects; all side effects are expanded only once, and prior to
+visiting any list element. On the other hand, the fact that unquoted
+macros are expanded exactly once means that macros without side effects
+can be used to generate lists. For example,
+
+@example
+m4_foreach([i], [[1], [2], [3]m4_errprintn([hi])], [i])
+@error{}hi
+@result{}123
+m4_define([list], [[1], [2], [3]])
+@result{}
+m4_foreach([i], [list], [i])
+@result{}123
+@end example
+
@defmac m4_car (@var{list})
@msindex{car}
Expands to the quoted first element of the comma-separated quoted
# -----------------
# Compare the two lists of integer expressions A and B.
#
+# m4_list_cmp takes care of any side effects; we only override
+# _m4_list_cmp_raw, where we can safely expand lists multiple times.
# First, insert padding so that both lists are the same length; the
# trailing +0 is necessary to handle a missing list. Next, create a
# temporary macro to perform pairwise comparisons until an inequality
# m4_eval([($2) != ($4)]), [1], [m4_cmp([$2], [$4])],
# [0]_m4_popdef([_m4_cmp], [_m4_size]))
# then calls _m4_cmp([1+0], [0], [1], [2+0])
-m4_define([m4_list_cmp],
-[m4_if([$1], [$2], 0,
- [m4_pushdef([_m4_size])_$0($1+0_m4_list_pad(m4_count($1), m4_count($2)),
+m4_define([_m4_list_cmp_raw],
+[m4_if([$1], [$2], 0, [m4_pushdef(
+ [_m4_size])_m4_list_cmp($1+0_m4_list_pad(m4_count($1), m4_count($2)),
$2+0_m4_list_pad(m4_count($2), m4_count($1)))])])
m4_define([_m4_list_pad],
# arguments.
#
# For m4_mapall_sep, merely expand the first iteration without the
-# separator, then include separator as part of subsequent recursion.
+# separator, then include separator as part of subsequent recursion;
+# but avoid extra expansion of LIST's side-effects via a helper macro.
# For m4_map_sep, things are trickier - we don't know if the first
# list element is an empty sublist, so we must define a self-modifying
# helper macro and use that as the separator instead.
[_m4_map([_m4_apply([m4_Sep([$2])[]$1]], [], $3)m4_popdef([m4_Sep])])
m4_define([m4_mapall_sep],
-[m4_if([$3], [], [],
- [m4_apply([$1], m4_car($3))_m4_map([m4_apply([$2[]$1]], $3)])])
+[m4_if([$3], [], [], [_$0([$1], [$2], $3)])])
+
+m4_define([_m4_mapall_sep],
+[m4_apply([$1], [$3])_m4_map([m4_apply([$2[]$1]], m4_shift2($@))])
# _m4_map(PREFIX, IGNORED, SUBLIST, ...)
# --------------------------------------
# long lists, since less text is being expanded for deciding when to end
# recursion. The recursion is between a pair of macros that alternate
# which list is trimmed by one element; this is more efficient than
-# calling m4_cdr on both lists from a single macro.
+# calling m4_cdr on both lists from a single macro. Guarantee exactly
+# one expansion of both lists' side effects.
m4_define([m4_list_cmp],
+[_$0_raw(m4_dquote($1), m4_dquote($2))])
+
+m4_define([_m4_list_cmp_raw],
[m4_if([$1], [$2], [0], [_m4_list_cmp_1([$1], $2)])])
m4_define([_m4_list_cmp],
[m4_if([$1], [], [0m4_ignore], [$2], [0], [m4_unquote], [$2m4_ignore])])
m4_define([_m4_list_cmp_1],
-[_m4_list_cmp_2([$2], m4_dquote(m4_shift2($@)), $1)])
+[_m4_list_cmp_2([$2], [m4_shift2($@)], $1)])
m4_define([_m4_list_cmp_2],
[_m4_list_cmp([$1$3], m4_cmp([$3+0], [$1+0]))(
# -1 if VERSION-1 < VERSION-2
# 0 if =
# 1 if >
+#
+# Since _m4_version_unletter does not output side effects, we can
+# safely bypass the overhead of m4_version_cmp.
m4_define([m4_version_compare],
-[m4_list_cmp(_m4_version_unletter([$1]), _m4_version_unletter([$2]))])
+[_m4_list_cmp_raw(_m4_version_unletter([$1]), _m4_version_unletter([$2]))])
# m4_PACKAGE_NAME
m4_version_compare([1z], [1aa])
m4_version_compare([2.61a], [2.61a-248-dc51])
m4_version_compare([2.61b], [2.61a-248-dc51])
+dnl Test that side effects to m4_list_cmp occur exactly once
+m4_list_cmp([[0], [0], [0]m4_errprintn([hi])],
+ [[0], [0], [0]m4_errprintn([hi])])
+m4_list_cmp([[0], [0], [0]m4_errprintn([hi])],
+ [[0], [0], [0]m4_errprintn([bye])])
]],
[[-1
1
-1
-1
1
+0
+0
+]], [[hi
+hi
+hi
+bye
]])
AT_CLEANUP
AT_SETUP([M4 loops])
+AT_KEYWORDS([m4@&t@_for m4@&t@_foreach m4@&t@_foreach_w])
+
AT_CHECK_M4SUGAR_TEXT([[dnl
m4_define([myvar], [outer value])dnl
m4_for([myvar], 1, 3, 1, [ myvar])
m4_foreach_w([myvar], [a b c, d,e f
g], [ myvar|])
myvar
+dnl only one side effect expansion, prior to visiting list elements
+m4_foreach([i], [[1], [2], [3]m4_errprintn([hi])], [m4_errprintn(i)])dnl
]],
[[ 1 2 3
1 2 3
| f|
a| b| c,| d,e| f| g|
outer value
-]], [])
+]], [[hi
+1
+2
+3
+]])
AT_DATA_M4SUGAR([script.4s],
[[m4_init
m4_define([pass1], [oops])dnl
m4_map([a], [[[a]]])1
m4_map([m4_unquote([a])], [m4_dquote([a])])
+dnl only one side effect expansion, prior to visiting list elements
+m4_map([m4_errprintn], [[[1]], [[2]], [[3]]m4_errprintn([hi])])dnl
+m4_map_sep([m4_errprintn], [], [[[1]], [[2]], [[3]]m4_errprintn([hi])])dnl
+m4_mapall([m4_errprintn], [[[1]], [[2]], [[3]]m4_errprintn([hi])])dnl
+m4_mapall_sep([m4_errprintn], [], [[[1]], [[2]], [[3]]m4_errprintn([hi])])dnl
]],
[[
1 2
-
pass1
pass
-]], [])
+]], [[hi
+1
+2
+3
+hi
+1
+2
+3
+hi
+1
+2
+3
+hi
+1
+2
+3
+]])
AT_CLEANUP
m4_bpatsubsts([a1]m4_for([i], [1], [10000], [], [,i]), [a2], [A])
m4_bmatch([9997]m4_for([i], [1], [10000], [], [,^i$]))
m4_define([up], [m4_define([$1], m4_incr($1))$1])m4_define([j], 0)dnl
-m4_cond(m4_for([i], [1], [10000], [], [[up([j])], [9990], i,]) [oops])
+m4_cond(m4_for([i], [1], [10000], [], [[up([j])], [9990], i,]) [oops]) j
m4_count(m4_transform_pair([,m4_quote], []m4_transform([,m4_echo]m4_for([i],
[1], [10000], [], [,i]))))
m4_divert_pop(0)
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