Re: FW: divert(-1) does not work in argument

[re-adding the list with permission]

On 11/18/19 3:17 PM, Ice Ninja wrote:
> Hi Eric,
> 
>>
>> So the key thing here, looks to me, is the stream and the action of
>> collecting arguments phase is ignoring the stream where the text actually
>> is wrapped in.

The output stream is ONLY relevant to outer-most macro expansion.  All 
nested macro expansion during argument collection affect only what 
argument is collected, not what is output.

>>
>> I could work around the 'unexpected' or 'unituitive' behavior with
>> 'ignore' definition like this,
>> enswan@ws/m4$ m4
>> <<<'changequote()changequote([,])define(ignore)include(ignore(good)show)'
>> m4:stdin:1: cannot open `show': No such file or directory

Yes, an ignore macro is one way to ignore arbitrary text regardless of 
whether it is expanded as an outermost macro or as a nested expansion 
during argument collection.

>>
>> Shouldn't the argument expansion phase also respects the end result of the
>> expansion including respect the stream?

During argument collection, there is no output stream, only the argument 
being collected.  There are no diversions in play except during 
outermost macros.

>> If not, when the argument itself is
>> an independent m4 script, the logic of 'running' that script will be
>> undergone a different mechanism which hence requires extra attention and
>> effort to deal with.

Parsing an m4 script in argument collection context is indeed different 
than parsing the same script in top-level context.  But that's an 
inherent design limitation of the m4 language, so not something we can 
really change.

>>
>> I had no problem regards to the 1st m4 call in the last email,
>>> enswan@ws/bin$ m4
>> <<<'changequote()changequote([,])divert(-1)good[]divert[]show'
>>> show
>> I had it there was to show the inconsistency between the calls of m4 with
>> the same piece of code .
>>
>> Do you have a bit feeling that my suggestion is reasonable or I should
>> correct myself entirely to 'think' in the way it is?

As I don't see m4 code changing, then it does seem like you'll have to 
adjust your thinking on how argument collection works.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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