Haskell Platform Proposal: add transformers and revise the mtl package to depend on it

[Ross Paterson]

On Tue, Nov 02, 2010 at 02:10:36PM +0100, Johan Tibell wrote:
> On Tue, Nov 2, 2010 at 1:45 PM, Ross Paterson <ross at soi.city.ac.uk> wrote:
> > On Mon, Oct 25, 2010 at 09:21:44AM +0100, Ross Paterson wrote:
> >> This has been up for over 5 weeks, with no dissent (except for a proposal
> >> to obsolete mtl in favour of monads-fd).
> >>
> >> I think the next step would be to upload the tarball of mtl-2.0, which
> >> I propose to do soon.
> >
> > I uploaded mtl-2.0.0.0 to hackage last week.
> >
> > What is the next step on the HP side?  By my reading of the procedure,
> > it needs action from the steering committee.
> 
> Wouldn't the next steps be to update all the libraries in the platform
> to use mtl-2?

The ones that depend on mtl are:

  cgi-3001.1.7.3 (latest version 3001.1.8.1)
  fgl-5.4.2.3
  QuickCheck-2.1.1.1 (latest version 2.3.0.2)
  regex-base-0.93.2
  regex-compat-0.93.1
  regex-posix-0.94.2
  HTTP-4000.0.9 (latest version 4000.0.10)

Assuming the latest version of HTTP is included, they all build unchanged
with mtl-2.0.0.0 except for cgi-3001.1.8.1.  That requires a small change
to line 58 of Network/CGI/Monad.hs:

  instance Monad m => Functor (CGIT m) where

Changing Monad to Functor will get it working with mtl >= 2, or change
Monad m to (Functor m, Monad m) to work with old and new versions of mtl.