[Haskell-cafe] Why no IO transformer monad?

[Keean Schupke]

What about:

    runIOT :: Monad m => IOT m a -> IO (m a)

Keean.

Udo Stenzel wrote:

>Henning Sato von Rosen <henning.von.rosen at gmail.com> schrieb am 18.12.04 18:31:11:
>  
>
>>For each basic monad there seems to be a corresponding transformer,
>>e.g.  'StateT' for 'State' and so on.
>>    
>>
>
>To be useful every transformer has a "run" method of some kind.  For a hypothetical
>IO transformer it would look like
>
>runIOT :: Monad m => IOT m a -> m a
>
>...which is basically the same as unsafePerformIO and defeats the purpose of
>having an IO Monad at all.  If you want to retain the IO-type in the result, then
>you don't need IOT at all, layering any transformer on top of IO is exactly what's
>needed.
>
>
>Udo.
>
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