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A few more m4sugar improvements, to benefit libtool.
* lib/m4sugar/m4sugar.m4 (m4_bpatsubsts, _m4_shiftn): Reduce size of expansion by avoiding extra uses of $@. (m4_shiftn): Avoid extra dnl, and forbid shifting by 0. (_m4_cdr): New helper macro. (_m4_map, m4_map_sep): Use it to reduce size of expansion. (_m4_shift3): New helper macro. (_m4_foreach): Swap argument order, and use new macro to reduce size of expansion. * doc/autoconf.texi (Looping constructs) <m4_shiftn>: Mention that count must be positive. Signed-off-by: Eric Blake <ebb9@byu.net>
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Eric Blake
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ChangeLog
12
ChangeLog
@ -1,5 +1,17 @@
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2007-10-16 Eric Blake <ebb9@byu.net>
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A few more m4sugar improvements, to benefit libtool.
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* lib/m4sugar/m4sugar.m4 (m4_bpatsubsts, _m4_shiftn): Reduce size
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of expansion by avoiding extra uses of $@.
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(m4_shiftn): Avoid extra dnl, and forbid shifting by 0.
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(_m4_cdr): New helper macro.
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(_m4_map, m4_map_sep): Use it to reduce size of expansion.
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(_m4_shift3): New helper macro.
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(_m4_foreach): Swap argument order, and use new macro to reduce
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size of expansion.
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* doc/autoconf.texi (Looping constructs) <m4_shiftn>: Mention that
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count must be positive.
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* doc/autoconf.texi (Evaluation Macros) <m4_expand>: Fix typo.
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Reported by Ralf Wildenhues.
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@ -10670,7 +10670,8 @@ The deprecated macro @code{AC_FOREACH} is an alias of
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@msindex{shiftn}
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@code{m4_shiftn} performs @var{count} iterations of @code{m4_shift},
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along with validation that enough arguments were passed in to match the
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shift count. @code{m4_shift2} and @code{m4_shift3} are specializations
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shift count, and that the count is positive. @code{m4_shift2} and
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@code{m4_shift3} are specializations
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of @code{m4_shiftn}, introduced in Autoconf 2.62, and are more efficient
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for two and three shifts, respectively.
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@end defmac
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@ -398,6 +398,18 @@ m4_define([m4_cdr],
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[$#], 1, [],
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[m4_dquote(m4_shift($@))])])
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# _m4_cdr(LIST)
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# -------------
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# Like m4_cdr, except include a leading comma unless only one element
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# remains. Why? Because comparing a large list against [] is more
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# expensive in expansion time than comparing the number of arguments; so
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# _m4_cdr can be used to reduce the number of arguments when it is time
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# to end recursion.
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m4_define([_m4_cdr],
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[m4_if([$#], 1, [],
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[, m4_dquote(m4_shift($@))])])
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# m4_cond(TEST1, VAL1, IF-VAL1, TEST2, VAL2, IF-VAL2, ..., [DEFAULT])
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# -------------------------------------------------------------------
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@ -439,13 +451,12 @@ m4_define([m4_cond],
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# -------------------
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# Invoke MACRO($1), MACRO($2) etc. where $1, $2... are the elements
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# of LIST (which can be lists themselves, for multiple arguments MACROs).
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m4_define([m4_fst], [$1])
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m4_define([m4_map],
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[m4_if([$2], [[]], [],
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[_m4_map([$1], [$2])])])
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m4_define([_m4_map],
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[m4_ifval([$2],
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[$1(m4_fst($2))[]_m4_map([$1], m4_cdr($2))])])
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[m4_if([$#], [1], [],
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[$1(m4_unquote(m4_car($2)))[]_m4_map([$1]_m4_cdr($2))])])
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# m4_map_sep(MACRO, SEPARATOR, LIST)
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@ -455,7 +466,7 @@ m4_define([_m4_map],
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# arguments MACROs).
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m4_define([m4_map_sep],
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[m4_if([$3], [[]], [],
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[$1(m4_fst($3))[]_m4_map([$2[]$1], m4_cdr($3))])])
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[$1(m4_unquote(m4_car($3)))[]_m4_map([$2[]$1]_m4_cdr($3))])])
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## ---------------------------------------- ##
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@ -483,7 +494,7 @@ m4_define([m4_map_sep],
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m4_define([m4_bpatsubsts],
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[m4_if([$#], 0, [m4_fatal([$0: too few arguments: $#])],
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[$#], 1, [m4_fatal([$0: too few arguments: $#: $1])],
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[$#], 2, [m4_builtin([patsubst], $@)],
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[$#], 2, [m4_builtin([patsubst], [$1], [$2])],
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[_$0($@m4_if(m4_eval($# & 1), 0, [,]))])])
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m4_define([_m4_bpatsubsts],
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[m4_if([$#], 2, [$1],
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@ -565,14 +576,24 @@ m4_define([m4_popdef],
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# m4_shiftn(N, ...)
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# -----------------
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# Returns ... shifted N times. Useful for recursive "varargs" constructs.
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#
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# Autoconf does not use this macro, because it is inherently slower than
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# calling the common cases of m4_shift2 or m4_shift3 directly. But it
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# might as well be fast for other clients, such as Libtool. One way to
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# do this is to expand $@ only once in _m4_shiftn (otherwise, for long
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# lists, the expansion of m4_if takes twice as much memory as what the
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# list itself occupies, only to throw away the unused branch). The end
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# result is strictly equivalent to
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# m4_if([$1], 1, [m4_shift(,m4_shift(m4_shift($@)))],
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# [_m4_shiftn(m4_decr([$1]), m4_shift(m4_shift($@)))])
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# but with the final `m4_shift(m4_shift($@)))' shared between the two
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# paths. The first leg uses a no-op m4_shift(,$@) to balance out the ().
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m4_define([m4_shiftn],
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[m4_assert(0 <= $1 && $1 < $#)dnl
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_m4_shiftn($@)])
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[m4_assert(0 < $1 && $1 < $#)_$0($@)])
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m4_define([_m4_shiftn],
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[m4_if([$1], 0,
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[m4_shift($@)],
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[_m4_shiftn(m4_eval([$1]-1), m4_shift(m4_shift($@)))])])
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[m4_if([$1], 1, [m4_shift(],
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[$0(m4_decr([$1])]), m4_shift(m4_shift($@)))])
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# m4_shift2(...)
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# m4_shift3(...)
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@ -581,6 +602,17 @@ m4_define([_m4_shiftn],
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m4_define([m4_shift2], [m4_shift(m4_shift($@))])
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m4_define([m4_shift3], [m4_shift(m4_shift(m4_shift($@)))])
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# _m4_shift3(...)
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# ---------------
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# Like m4_shift3, except include a leading comma unless there were exactly
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# three arguments. Why? Because in recursion, it is nice to distinguish
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# between 1 element left and 0 elements left, based on how many arguments
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# this shift expands to.
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m4_define([_m4_shift3],
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[m4_if([$#], [3], [],
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[, m4_shift(m4_shift(m4_shift($@)))])])
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# m4_undefine(NAME)
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# -----------------
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# Like the original, except don't tolerate undefining something which is
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@ -827,13 +859,18 @@ m4_if(m4_defn([$1]), [$2], [],
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# => -active--active-
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#
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# This macro is called frequently, so avoid extra expansions such as
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# m4_ifval and dnl.
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# m4_ifval and dnl. Also, since $2 might be quite large, try to use it
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# as little as possible in _m4_foreach; each extra use requires that much
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# more memory for expansion. So, rather than directly compare $2 against
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# [] and use m4_car/m4_cdr for recursion, we instead unbox the list (which
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# requires swapping the argument order in the helper) and use _m4_shift3
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# to detect when recursion is complete.
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m4_define([m4_foreach],
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[m4_pushdef([$1])_$0($@)m4_popdef([$1])])
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[m4_pushdef([$1])_$0([$1], [$3]m4_if([$2], [], [], [, $2]))m4_popdef([$1])])
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m4_define([_m4_foreach],
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[m4_if([$2], [], [],
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[m4_define([$1], m4_car($2))$3[]$0([$1], m4_cdr($2), [$3])])])
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[m4_if([$#], [2], [],
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[m4_define([$1], [$3])$2[]$0([$1], [$2]_m4_shift3($@))])])
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# m4_foreach_w(VARIABLE, LIST, EXPRESSION)
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