Re: [Haskell-cafe] Problem with own written monad

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Yes. It's simply impossible. The Stack data type can't be turned into a monad. Why not? Surely this is just a variation on the theme of a state monad?

Because it can't be turned into a functor. You can't, given a function a -> b, construct a function Stack a -> Stack b. On the contrast, you can easily construct a function State z a -> State z b.