Re: m4sugar speedups

[Eric Blake]

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According to Benoit SIGOURE on 10/26/2007 12:56 AM:
>> address@hidden m4_car (@var{list})
>> address@hidden
>> +Expands to the quoted first element of the comma-separated quoted
>> address@hidden  Often used with @code{m4_cdr} to recursively iterate
>> +through a list.  Generally, when using quoted lists of quoted elements,
>> address@hidden should be called without any extra quotes.
>> address@hidden defmac
>> +
>> address@hidden m4_cdr (@var{list})
>> address@hidden
>> +Expands to a quoted list of all but the first element of the
>> +comma-separated quoted @var{list}, or the empty string if @var{list} had
>> +only one element.  Generally, when using quoted lists of quoted
>> +elements, @code{m4_cdr} should be called without any extra quotes.
> 
> May I ask why `car' and `cdr'?

Pre-existing macro names, already in use (even though they were
undocumented) by at least libtool.  I suppose we could choose better names
(m4_first and m4_rest), and keep the m4_car and m4_cdr name as
undocumented aliases.  Plus the terms car and cdr have a history in lisp
programming, and m4sugar tends to look distantly related to lisp (hmm,
even 'info elisp "list elements"' fails to give a history behind these
names :(  But wikipedia does: http://en.wikipedia.org/wiki/CAR_and_CDR.
The names go back to the 50s (way before my time!) because of the
'contents of address register' and 'contents of decrement register' on the
IBM 704 machine).

>> address@hidden
>> +m4_define([m4_map], [m4_if([$2], [[]], [], [_$0($@@)])])dnl
>> +m4_define([_m4_map], [m4_ifval([$2],
>> +  [$1(m4_unquote(m4_car($2)))[]$0([$1], m4_cdr($2))])])dnl
>> +m4_map([ m4_eval], [[1],[1+1]])
>            ^
> Why is there a space here?  I'm just asking :D

So that the result will be " 1 2" and not "12".  Plus, to emphasize that
m4_indir would invoke the macro named " m4_eval", while m4_map/m4_apply
output a literal " " followed by the invocation of "m4_eval".  Do I need
to add more words along those lines here?

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

Eric Blake             address@hidden
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