[Haskell-cafe] What is your favourite Haskell "aha" moment?

[Vanessa McHale]

I'm not sure I follow. Do you mean that IO is not a monad because
equivalence of values cannot be defined? Or is it something deeper?

On 07/11/2018 05:19 PM, Conal Elliott wrote:
> > The fact that you can define the IO monad in Haskell was quite a
> revelation.
>
> But it's *not* a fact. It's a lie. And one of the most devious sort,
> since the source code appears to agree. The purported definition
> couldn't possibly explain concurrency.
>
> On Wed, Jul 11, 2018 at 7:21 AM, Vanessa McHale
> <vanessa.mchale at iohk.io <mailto:vanessa.mchale at iohk.io>> wrote:
>
>     I find it quite elegant! The fact that you can define the IO monad
>     in Haskell was quite a revelation. And it's especially nice when
>     paired with a demonstration of C FFI (where you might *need* to
>     sequence side effects such as freeing a value after it has been read).
>
>     newtypeIO
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Types.html#IO>a
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Types.html#local-6989586621679009802>=IO
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Types.html#IO>(State#
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Prim.html#State%23>RealWorld
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Prim.html#RealWorld>->(#State#
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Prim.html#State%23>RealWorld
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Prim.html#RealWorld>,a
>     <http://hackage.haskell.org/package/ghc-prim-0.5.2.0/docs/src/GHC.Types.html#local-6989586621679009802>#))
>
>
>     On 07/11/2018 09:14 AM, Stefan Monnier wrote:
>>>     In a few weeks I'm giving a talk to a bunch of genomics folk at the Sanger
>>>     Institute<https://www.sanger.ac.uk/> <https://www.sanger.ac.uk/> about Haskell.   They do lots of
>>>     programming, but they aren't computer scientists.
>>>     I can tell them plenty about Haskell, but I'm ill-equipped to answer the
>>>     main question in their minds: why should I even care about Haskell?  I'm too
>>>     much of a biased witness.
>>     I don't much like the monad solution for side-effects, but if those guys
>>     might have some knowledge of the horror of concurrent programming with
>>     locks, the STM system would be a good candidate.
>>
>>
>>             Stefan
>>
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>
>     -- 
>
>
>
>     *Vanessa McHale*
>     Functional Compiler Engineer | Chicago, IL
>
>     Website: www.iohk.io <http://iohk.io>
>     Twitter: @vamchale
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