[darcs-users] [Haskell-cafe] Poll: Do you need to be able to build darcs from source on GHC 6.6?

[Jason Dagit]

On Wed, Oct 29, 2008 at 8:01 AM, David Roundy <droundy at darcs.net> wrote:
> On Wed, Oct 29, 2008 at 11:17:35AM -0000, Mitchell, Neil wrote:
>> Duncan,
>>
>> I believe the major darcs issue is the changed GADT implementation
>> between 6.6, so that neither 6.6 or 6.8 is a superset/subset of the
>> other - leading to a situation where they have to use a common subset of
>> both.
>
> No, the 6.6 gadts are nicer than the 6.8 gadts, but the common subset
> is pretty large.

The 6.6 gadts had broken type checking though as Simon Peyton-Jones
has pointed out before.  There is even a paper on why and what had to
be done to fix the problem.  See here for more details:
http://research.microsoft.com/~simonpj/papers/gadt/index.htm

I do agree that the polymorphic nature of let/where makes it harder to
use GADTs now that the type checker has been fixed but without
introducing new syntax just for GADTs (which isn't a bad idea) I'm not
sure what else can be done.

Jason