[Haskell-cafe] Re: A monad using IO, Reader, Writer, State and Error

Martin Huschenbett huschi at gmx.org
Fri Apr 13 13:55:52 EDT 2007

Chris Kuklewicz schrieb:
> Martin Huschenbett wrote:
>> 1) type MyMonad = ErrorT E (RWST R W S IO)
>> 2) type MyMonad = RWST R W S (ErrorT E IO)
> So (1) gives (Left e,s,w) or (Right a,s,w)
> and (2) gives (Left e) or (Right (a,s,w))

Due to this fact i decided to use (1). If the operation fails and I get 
(Left e,s,w) what are the values of 's' and 'w'? Are they the state and 
the written things that were produced by the last successfull operation?



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