Migrating D front end to D - post Dconf

[Daniel Murphy]

"David Nadlinger" <see at klickverbot.at> wrote in message 
news:llovknbpvcnksinsnpfk at forum.dlang.org...
> On Saturday, 11 May 2013 at 15:16:29 UTC, Daniel Murphy wrote:
>> "Iain Buclaw" <ibuclaw at ubuntu.com> wrote in message
>> news:mailman.1201.1368284962.4724.digitalmars-d at puremagic.com...
>>>
>>> Actually, the more I sit down and think about it, the more I question
>>> whether or not it is a good idea for the D D front end to have a 
>>> dependency
>>> on phobos.   Maybe I should stop thinking in general.  :)
>>>
>>
>> Yeah, the compiler can't depend on phobos.
>
> Why?
>
> If we keep a "must compile with several past versions" policy anyway, what 
> would make Phobos special?
>
> David

Yes it's possible, but it seems like a really bad idea because:
- Phobos is huge
- Changes in phobos now have the potential to break the compiler

If you decide that all later versions of the compiler must compile with all 
earlier versions of phobos, then those phobos modules are unable to change.

If you do it the other way and say old versions of the compiler must be able 
to compile the newer compilers and their versions of phobos, you've locked 
phobos to an old subset of D.  (And effectively made the compiler source 
base enormous)

The nice middle ground is you take the chunk of phobos you need, add it to 
the compiler source, and say 'this must always compile with earlier versions 
of the compiler'.