[Haskell-cafe] Monad transformer to consume a list

[Henning Thielemann]

On Mon, 6 Apr 2009, Stephan Friedrichs wrote:

> Hello,
>
> is there a monad transformer to consume an input list? I've got external
> events "streaming into the monad" that are consumed on demand and I'm
> not sure if there's something better than a StateT.

I wondered that, too. I wondered whether there is something inverse to 
Writer, and Reader is appearently not the answer. Now I think, that State 
is indeed the way to go to consume a list. Even better is StateT List 
Maybe:

next :: StateT [a] Maybe a
next = StateT Data.List.HT.viewL   -- see utility-ht package