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Using Arrows for Dependency Handling

• leif 17y ago
  If anyone can explain to me why monads are insufficient, that would be swell. I'm really not going to get it on my own any time soon.
  • jaspervdj 17y ago
    Author of the article here. I'll try to give a quick informal explanation. If you look at the type signature of `>>=`: m a -> (a -> m b) -> m b Let's suppose there's a HakyllAction monad. The >>= signature would be: HakyllAction a -> (a -> HakyllAction b) -> HakyllAction b If we implement this operator, we get a value `HakyllAction a` and a function `a -> HakyllAction b`. We can look at the dependencies of the value, but we don't have access to the dependencies of the `a -> HakyllAction b`. If we want that, we need to apply it to the first value. This goes against the idea of dependency handling -- we want to know the dependencies first, and then only execute the function if needed. Hope this helps.
    • leif 17y ago
      This helps very much, thanks! :)