The purported definition also mixes very badly with strictness analysis. For IO, m >>= f should be *lazy* in f (e.g., print 3 >> undefined should print 3 before throwing an exception) but the purported definition would suggest it's *strict* (print 3 >> undefined is equivalent to undefined).

On Wed, Jul 11, 2018, 6:20 PM Conal Elliott <conal@conal.net> 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@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).

newtype IO a = IO (State# RealWorld -> (# State# RealWorld, a #))

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/> 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
Twitter: @vamchale
PGP Key ID: 4209B7B5

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