Show HN: Legion, an as-simple-as-possible blockchain server written in Haskell

I&#x27;m tempted to just make a youtube video going over this code line by line.<p>It&#x27;s a really great introduction to a non-trivial bit of Haskell.

Great use of distributed-process and distributed-process-p2p! Being able to access service discovery and peer-to-peer communication as simple Haskell packages is kind of amazing.<p>* <a href="https:&#x2F;&#x2F;hackage.haskell.org&#x2F;package&#x2F;distributed-process-p2p" rel="nofollow">https:&#x2F;&#x2F;hackage.haskell.org&#x2F;package&#x2F;distributed-process-p2p</a><p>* <a href="https:&#x2F;&#x2F;hackage.haskell.org&#x2F;package&#x2F;distributed-process" rel="nofollow">https:&#x2F;&#x2F;hackage.haskell.org&#x2F;package&#x2F;distributed-process</a>

I had a brief look through, and it looks like there&#x27;s no proof-of-work in the mining?<p>What stops somebody from rewriting history and passing it off as legitimate?

Neat. Just browsing through the source, is there a reason that:<p><pre><code> calculateBlockHash (Block i p t b _) = concatMap hashString [show i, p, show t, b] </code></pre> is not<p><pre><code> calculateBlockHash (Block i p t b _) = hashString $ concat [show i, p, show t, b] </code></pre> i.e. why is a block hash a concatenation of 4 SHA-256 hashes instead of just 1? Is there some security benefit of doing it one way vs. the other?<p>edit: thinking about it a little more, option 2 seems better because in option 1 you can calculate 3&#x2F;4 of a block hash without knowing the previous block&#x27;s hash. Maybe that&#x27;s not a problem in this context though?

Of course there are name collisions everywhere, but, there&#x27;s a metacomputing&#x2F;grid computing&#x2F;distributed OS thingie named &quot;Legion&quot; from the University of Virginia that has a bunch of papers about it in the CS literature.<p>Oh, and we saw off the American Legion threatening to sue us by saying &quot;We&#x27;re the State of Virginia, go right ahead...&quot;; what&#x27;s your strategy? :-)

Nicely done. It reads like Ikea instructions. I didn&#x27;t really know how blockchain worked until I read this code. If this was written as a teaching tool or a portfolio piece or even an art project, then I say its a big success.<p>One question:<p><pre><code> getBlockChain :: (SpockState m ~ BlockChainState, MonadIO m, HasSpock m) =&gt; m [Block] </code></pre> What does the squiggle mean?

My takeaway from this was to learn more about Literate Haskell. As somebody points out a Blockchain without a consensus mechanism is simply a linked list ie this is not really about pushing the envelope of Blockchain tech.

In case you&#x27;re not aware of it, also check out Haskoin, a Bitcoin implementation in Haskell.<p><a href="https:&#x2F;&#x2F;github.com&#x2F;haskoin&#x2F;haskoin" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;haskoin&#x2F;haskoin</a>

Can someone explain to me in short summary why blockchain without crypto currency suddenly is a thing and why anybody would want it?

Thanks for sharing, the code looks very elegant. This alone makes me want to sit down and learn Haskell.

... had this been written in a language less esoteric than Haskell, it would&#x27;ve been even better for the rest of us :)