According to neil.mowb...@calgacus.com on 1/7/2010 1:44 PM: > Folks, > > Is it possible to access macro arguments using an expression?
Yes, if you use an intermediate macro. > For example, using m4sugar's m4_for() In fact, m4sugar's m4_for is doing something exactly like that in its under-the-hood implementation, at least when targetting m4 1.4.x. If you want a study in the black magic possible with GNU m4, read the file lib/m4sugar/foreach.m4 that ships with autoconf 2.64 or newer. > m4_define([m4__print_arguments], > [m4_for([aArg], 1, $#, +1, [ aArg = $aArg ])]) > > m4__print_arguments(A, B, C, D, E) > > And have the expression $aArg evalute to values of $1, $2 ... as > the macro aArg ranges over 1,2, .... That is, have the above produce > > 1 = A 2 = B 3 = C Here's one way. dnl argn(N,args) - print the Nth argument of ARGS, provided that N > 0 m4_define([argn], [m4_pushdef([_], [m4_popdef([_])[$$1]])_(m4_shift($@))]) m4_define([m4__print_arguments], [m4_for([aArg], 1, $#, +1, [ aArg = argn(aArg, $@) ])]) m4__print_arguments(A, B, C, D, E) However, it is not necessarily the most efficient, since you are passing $@ through every iteration of m4_for. A more efficient approach, using modern m4sugar constructs, would be: m4_define([_m4__print_arguments], [m4_define([_],m4_incr(_)) _ = $1 ]) m4_define([m4__print_arguments], [m4_pushdef([_],[0])m4_map_args([_$0], $@)m4_popdef([_])]) m4__print_arguments(A, B, C, D, E) using _ as the incrementing counter to track how many arguments have been visited during m4_map_args. -- Don't work too hard, make some time for fun as well! Eric Blake e...@byu.net
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