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Comment by mitchty | Hacker News Reader

> * when you look for concurrent haskell you're directed towards the corresponding paper, "tackling the awkward squad" and a world of Async, MVar, ThreadId, STM and various types of Chan, and at that point you still can't write a line of concurrent haskell

I was directed here: http://community.haskell.org/~simonmar/pcph/

And after reading the first few chapters, I'd place go's options under the Rich Hickey quote of simple versus easy. Additionally I sped up a simulated annealing program with the accelerate framework in Haskell by typing "Acc " twice. From 1 000 iterations/minute to about 500 000. I'd call that an easy win. Haskell also allows for more than simply concurrent programming. I always ended up with locks in go and wondering why I was using it over c with an event loop and threads at that point.

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Haskell's concurrency advantage is that the answer to the question "Does Haskell have X concurrency construct?" is "yes", and additionally, it's generally safe to use because everything is immutable. It even has support for things that have proved difficult or impossible in almost every other context because of that immutability, most notably STM.

Haskell's concurrency disadvantage is the same set of answers to the same question. It intrinsically has a big toolbox to start with, and a bigger one once you get into the libraries that implement further things on top of it (the pipe libraries, for instance), and that intrinsically makes it harder.

So, for instance, yes, you certainly sped up your program very easily, but new users often have a hard time finding their way to the best resources, and if their problem is not a trivially parallelizable algorithm, which it sounds like you had, there can still be some trouble in figuring out which concurrency construct they need.

STM is useless with full immutability: it is safe in Haskell because effects (including mutation) can be controlled/packaged into contained areas, via abstractions like monads.

That said, one downside of STM is that it isn't as efficient as some other schemes especially with high contention, as everything gets serialized through the metadata for tracking transactions. It's an awesome tool, but not a panacea (like with any other technology).

(I'm sure you know this, but others reading the thread may not.)

Yeah, also the STM support is often overlooked and is a good fit for some tasks where everything else is much harder.

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