list monad transformer

[Andrew J Bromage]

G'day all.

On Thu, May 15, 2003 at 11:12:32AM -0700, Iavor Diatchki wrote:

> given that, we should either remove the 
> #ListT# transformer from the monad library, or (perhaps better) put a 
> big warning that it should only be used with commutative monads.

My personal choice would be to dump it and replace it with Ralf
Hinze's backtracking monad transformer, which _does_ preserve
commutativity.  If someone with checkin rights is listening in,
I'd be very happy to contribute my implementation, which is about
as stable as it's ever going to be.

Cheers,
Andrew Bromage