Re: [Flex-devel] Questions about functionality

[Joe K. <kr...@ni...>]

Aaron Stone wrote:
> 
> On Oct 14, 2008, at 8:45 AM, Joe Krahn wrote:
> 
>> What part of the generated code is supposed to be visible to user code
>> from section 1? My understanding is that section 1 is meant for
>> including extra headers, and inserting cpp #defines to modify cpp-based
>> options. However, it apparently does not come early enough in the
>> generated code, because somebody added the %top{} feature.
>>
>> My first guess is just to avoid moving any code to the other side of the
>> current section 1 code insertion, to avoid breaking things. But, there
>> should be some specific rules. In any case, the %top{} feature is useful
>> because it gets written to the public header.
> 
> Huh, ok. I seem to recall that stuff in the top section came very nearly 
> the beginning, if not actually the beginning, of the output file. I 
> wonder if there are assumptions of this in many scanners.
The problem is that location of section 1 code is ill-defined. It was 
created mainly to include headers, prototypes and macros needed in the 
actions. Those declarations should all include their own prerequisite 
headers. For that reason, section 1 could be inserted at the very top, 
which would avoid the need for %top{}. In fact, that makes the most 
sense to me, because Flex documentation never claims to make anything 
available to section 1 code, and is also how Flex's internal scanner 
source is written. But, that would surely break a lot of scanners, which 
are usually built by trial-and-error.

Other people may have different opinions that certain CPP definitions 
should be available, even if undocumented, based on experience with 
Flex. Even if the current plan is to just avoid changes that can break 
scanners, we should come up with a more precise definition of where 
section 1 code is inserted. My thinking is that section 1 code should 
really not depend on anything from Flex, except perhaps the version 
macros and standard I/O headers.

Joe