Compiler Versions

[Simon Marlow]

> Simon Marlow wrote (snipped):
> > I agree it's not worth arguing, it's more important to 
> decide whether we can implement Read Version.
> 
> Why is the Read instance for Version so important?  I don't really see
> one using it much.  The only occasion I can imagine when you 
> would actually
> want to create a Version value for GHC is when you send a new 
> release out the door.
> 
> I don't really the instance of Ord being that important 
> either.  What one
> wants to know is whether
> (1) version X was released later than some given date;
> (2) version X is lexicographically subsequent to [sequence of 
> integers]
>      (so GHC 6.02.1 comes after GHC 4.08.1);
> (3) version X is a subversion of [sequence of integers], as
>      6.2.1 is a subversion of 6.2;
> (4) version X has a tag attached meaning "DANGER.  Do not use 
> unless your
>      name is Simon".

I see - I assumed you were planning to have Ord and Read instances for
Version and compare versions by doing

   if ghc_version => read "6.2" then ...

but you'd do it like this:

   if branch ghc_version >= [6,2] then ...

which is fine.  In fact, I think I like yours better :-)

I'm not convinced of the need to have a date attached to all versions,
though.  Under what circumstances do you imagine needing (1) above,
where (2) won't do?

Cheers,
	Simon