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Comment by wireprotocol | Hacker News Reader

Thank you. I will look into these and give it another try.

It's a good point that maybe I should just have the right expectations here, and expect data structures to be hard in rust.

I looked around a bit and it looks like these thing are quite challenging in haskell as well.

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In Haskell it is easy, you can not create cyclic data structures ;-)

Huh? Sure you can.

Cyclic data structures can be created in Haskell, in large part due to laziness.

If you see data structures as cyclic, it is not "in large part due to laziness", but _only_ due to laziness. If you look at the memory representation I think (but I am not sure) there will be no cycles between allocated objects. Only a thunk.

Using strict data types, I think you agree that cycles can not be created. Non strict data structures I agree can be seen as cyclic, but I prefer seeing them as infinite.

Counterexample:

    $ ghci
    GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help
    Prelude> let ones = 1 : ones
    Prelude> take 50 ones
    [1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1]

You can take as many as you like. (The 'ones' list contains a tail which links back to its head, producing an infinite list.)

Obviously, this is a trivial example, you can do much more interesting things with mutually recursive bindings.

    let cycle = "cycle " ++ cycle

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