Stricter WriterT (Part II)

[Ross Paterson]

On Sun, Mar 17, 2013 at 09:18:13AM -0700, Gabriel Gonzalez wrote:
> So I propose that we add an additional stricter WriterT (under say,
> "Control.Monad.Trans.Writer.Stricter") which is internally
> implemented as StateT, but hide the constructor so we don't expose
> the implementation:
> 
> newtype WriterT w m a = WriterT { unWriterT :: w -> m (a, w) }

That would be slightly less transparent than the other transformers,
and it wouldn't be perfectly parallel to the existing versions of WriterT:
- the Applicative and Alternative instances would have different contexts
- there would be no Foldable or Traversable instances

On Tue, Mar 19, 2013 at 08:33:37PM -0400, Edward Kmett wrote:
> I use them fairly heavily, mostly so I can make packages that work with
> arbitrary transformer stacks.

There are several packages like this, that pass various stuff through all
the transformers.  Relatively few seem to use the strict writer for itself:

	alms darcswatch ghc-heap-view Glob GPipe-Collada Haschoo hbayes
	nemesis satchmo shake storable XmlHtmlWriter

I wonder if these users were expecting the linear behaviour that Gabriel
was exploring.

So perhaps the best thing would be to deprecate Writer.Strict in favour
of State.Strict.