[Haskell-cafe] Monadic correctness

[Andrew Coppin]

Daniel Fischer wrote:
> Am Samstag 17 Oktober 2009 22:24:08 schrieb Andrew Coppin:
>   
>> Edward Z. Yang wrote:
>>     
>>> Excerpts from Andrew Coppin's message of Sat Oct 17 15:21:28 -0400 2009:
>>>       
>>>> Suppose we have
>>>>
>>>>    newtype Foo x
>>>>    instance Monad Foo
>>>>    runFoo :: Foo x -> IO x
>>>>         
>
> Are you sure that's really the type you want for runFoo ?
> By the definition below, runFoo :: Foo x -> M -> IO x would be the natural type.
>   

M is a type containing a bunch of IORefs. runFoo generates M, feeds M to 
Foo x, and then does magical stuff with M afterwards.