I get the same strange inferred type for this quickly translated program: split [] = ([], []) split [h] = ([h], []) split (x:y:t) = let (s1, s2) = split t in (x:s1, y:s2) merge :: [Int] -> [Int] -> [Int] merge [] x = x merge x [] = x merge (h1:t1) (h2:t2) = if h1 < h2 then h1:merge t1 (h2:t2) else h2:merge (h1:t1) t2 sort [] = [] sort x = let (p, q) = split x in merge (sort p) (sort q) > :t sort sort :: [a] -> [Int] The reason is that sort always returns the empty list, independently of the input list, so the type of the input list is not constrained. On 29-03-2021 19:13, Henning Thielemann wrote:

On Mon, 29 Mar 2021, Antonio Regidor Garcia wrote:

...

Not bussiness oriented, but these two articles are pretty good at explaining what Haskell and similar languages have to offer:

This is brief and centered on Haskell's type system:

https://perl.plover.com/yak/typing/notes.html

From slide 29 on he gives the example that type inference can point him to an infinite loop.

This would not work in Haskell, would it? _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

El Mon, Mar 29, 2021 at 07:30:41PM +0200, Jaro Reinders escribió:

The reason is that sort always returns the empty list, independently of the input list, so the type of the input list is not constrained.

Actually, it only returns the empty list for the empty list. For other lists, it never returns.

XD XD XD It seems a sales talk about his STM monad, something like "Haskell is useless but Haskell+STM is in the good direction". So: Haskell 1.2 (stream-based IO): stateless, useless Haskell 1.3+ (monadic IO): statefull, but too coarse-grained, still useless Haskell 98/2010 + STM: more fine-grained statefullness, becoming usefull Best, Antonio El Mon, Mar 29, 2021 at 03:35:42PM +0800, YueCompl via Haskell-Cafe escribió:

https://www.reddit.com/r/programming/comments/25m291/simon_peyton_jones_hask... https://www.reddit.com/r/programming/comments/25m291/simon_peyton_jones_hask...

That might be sth you'd like to hide from the manager, but better prepared for himself to discover about.

Years have passed though, I'm very curious how situations have changed according to SPJ's criteria.

...

On 2021-03-29, at 08:24, Clinton Mead wrote:

I’m looking for recommendations of videos/articles to show to a software development manager about why one should use Haskell, focused more from a benefits to business perspective.

Naturally this may involve some code, this manager isn’t completely clueless when it comes to programming languages, but basically something that explains why I’m raving about this “Haskell” thing all the time and why it’s a good idea.

Thanks, Clinton _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

The STM is stateful (mutable state, thus impure) but it only changes the RAM, contrary to IO, that can change from the screen to missile launchers (so potentially much harmful). So the STM is deliberately separated from IO and similar monads. That's the point of using it. I don't have much experience combining it with non-IO monads, though. El Mon, Mar 29, 2021 at 07:11:49PM +0800, YueCompl escribió:

But AFAICT, STM composes poorly with other monads in today's mtl fashion, and by itself I don't think effects are tracked sufficiently well.

I'm not aware of an idiomatic way to properly have STM in a monad stack, or is it there?

...

On 2021-03-29, at 16:12, Antonio Regidor Garcia wrote:

XD XD XD It seems a sales talk about his STM monad, something like "Haskell is useless but Haskell+STM is in the good direction". So:

Haskell 1.2 (stream-based IO): stateless, useless Haskell 1.3+ (monadic IO): statefull, but too coarse-grained, still useless Haskell 98/2010 + STM: more fine-grained statefullness, becoming usefull

Best,

Antonio

El Mon, Mar 29, 2021 at 03:35:42PM +0800, YueCompl via Haskell-Cafe escribió:

...

https://www.reddit.com/r/programming/comments/25m291/simon_peyton_jones_hask... https://www.reddit.com/r/programming/comments/25m291/simon_peyton_jones_hask... <https://www.reddit.com/r/programming/comments/25m291/simon_peyton_jones_hask... https://www.reddit.com/r/programming/comments/25m291/simon_peyton_jones_hask...>

That might be sth you'd like to hide from the manager, but better prepared for himself to discover about.

Years have passed though, I'm very curious how situations have changed according to SPJ's criteria.

...

On 2021-03-29, at 08:24, Clinton Mead wrote:

I’m looking for recommendations of videos/articles to show to a software development manager about why one should use Haskell, focused more from a benefits to business perspective.

Naturally this may involve some code, this manager isn’t completely clueless when it comes to programming languages, but basically something that explains why I’m raving about this “Haskell” thing all the time and why it’s a good idea.

Thanks, Clinton _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

...

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

Thanks for the insights, I was not aware of this approach before. But with STM as the base monad, I feel like to have lost the ability to delimit transaction boundaries at will, which is the essential tool STM offers. I can only think of doing that from IO via `atomically`, but that way we are dragged back to write transaction composing code in IO, so will lose effect tracking. I dunno but is there a way to delimit STM transactions without IO?

On 2021-03-29, at 19:50, Viktor Dukhovni wrote:

STM is not a monad transformer, but it is a fine base monad, just like Identity, IO or ST. Here's a contrived example of (StateT Int STM Int):

import Control.Concurrent.STM import Control.Monad (when) import Control.Monad.Trans.State.Strict import Control.Monad.Trans.Class (lift)

-- main :: IO () main = do tv <- newTVarIO 0 y <- atomically $ flip evalStateT 0 $ do x <- get lift $ do modifyTVar tv (\a -> a + x + 1) y <- readTVar tv when (y > 10) retry return y print y

So any or all of RWST work with STM, but you typically want to keep your STM transactions small and simple, so this is not a place where one would generally run wild with fancy stacks that do non-trivial additional computation.

Indeed Monad Transformers are not Monads, they're always stacked on top of some base monad. The turtles don't go all the way down.

A practical example of STM-like Monad's can be found in Hasql, where database operations run in a Monad that ensures that they have no side-effects that would prevent the transaction from being retried on deadlock detection. This is also a base Monad, where if you like you can stack more (pure) transformers.

Which reminds me that ExceptT can be useful in such Monads, which avoid throwing impure exceptions. And is used in Hasql, where the operations tend to be more expensive than in STM, and any overhead from layering ExceptT or similar is quite small.

-- Viktor. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.