Re: [Haskell-cafe] Stacking monads - beginner design question

On Jan 30, 2008 12:44 AM, Adam Smyczek wrote:

Hi,

My application has to manage a data set. I assume the state monad is designed for this. The state changes in functions that: a. perform IO actions and b. return execution status and execution trace (right now I'm using WriteT for this).

Is the best solution: 1. to build a monad stack (for example State -> Writer -> IO) or 2. to use IORef for the data set or 3. something else?

Are monad stacks with 3 and more monads common? How could an example implementation look like?

Hi Adam, Indeed, this is quite common. You may be interested in reading http://cale.yi.org/index.php/How_To_Use_Monad_Transformers Good luck! -Brent