Re: [Haskell-cafe] Stateful iteratees

On Thu, Apr 7, 2011 at 7:04 PM, Ertugrul Soeylemez wrote:

Hello fellow Haskellers,

I'm trying to solve a very practical problem:  I need a stateful iteratee monad transformer.  Explicit state passing is very inconvenient and would destroy the elegance of my library.

There are two approaches to this:

 1. type MyT a m = Iteratee a (StateT MyConfig m)  2. type MyT a m = StateT MyConfig (Iteratee a m)

Both work well except in two very specific corner cases:

 - I need to convert the transformer to 'Iteratee a m', i.e. remove the    state layer.  This is obviously trivial with the second variant, but    seems very difficult with the first one, if it's possible at all.

Why can't you use #1 and do this when you call "run_"? G -- Gregory Collins