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

[Anders Kaseorg]

On Tue, 2 Nov 2010, Don Stewart wrote:
> Note that you've added MonadCatchIO as a dependency to cgi, which is 
> *not* part of the platform. This will prevent cgi being upgraded in the 
> next HP release.

Yeah, I added that in March with cgi 3001.1.8, in an effort to improve 
cgi’s exception handling situation [1].  Unfortunately, I learned a few 
weeks ago that MonadCatchIO is actually subtly broken [2], and although 
this problem does not affect cgi’s use of MonadCatchIO (with ReaderT and 
WriterT), it did throw a bit of a wrench into my plan to propose 
MonadCatchIO for addition to HP.

In fact, I have been working on a replacement for the MonadCatchIO 
functionality [3], which I hope will be awesome and could eventually end 
up in the transformers library.  I plan on uploading a package and 
announcing it within a day or so.

But I’m not sure whether it’s realistic to expect the community to be 
confident in the new package before the next HP freeze, so maybe the best 
option for now is to backport the fix and upload a cgi 3001.1.7.4?

[1] http://www.haskell.org/pipermail/libraries/2010-March/013169.html
[2] http://www.haskell.org/pipermail/haskell-cafe/2010-October/084890.html
[3] http://docs.yesodweb.com/blog/invertible-monads-exceptions-allocations/#disqus_thread
    (see comments)

Anders