[Haskell-cafe] Monadic correctness
andrewcoppin at btinternet.com
Sat Oct 17 17:32:29 EDT 2009
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.
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