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Comment by aviaviavi | Hacker News Reader

Yeah, it's for the compiler, otherwise it can't figure out that a BlockChainState is actually a SpockState m. I'm not really sure how it could otherwise, since the definition is completely decoupled from Spock.

It should be noted that it's entirely possible there's a less confusing way to write that type signature. I'm far from an expert in Haskell.

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I'm farther from an expert than you. I tried (and failed) to find a less confusing way...

One thing I see people doing when they have real gnarly type signature is to concentrate the horror in one place and paint a veneer of simplicity elsewhere:

    type Get stateType returnType
      = forall monad.
      (SpockState monad ~ stateType, MonadIO monad, HasSpock monad)
      => monad returnType

Then elsewhere:

    getBlockChain :: Get BlockChainState [Block]
    getLatestBlock :: Get BlockChainState Block

This may only help superficially as type errors will still be hard-to-understand.

Ah, I think this is a better though! If you got this working, feel free to open up a PR. Or I can look into it when I get time.

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