Paul Hudak wrote:
[I]n the one-of-many ways that I view monads, a monad is just a high-order function that abstracts away function composition. In particular, if I have an action f, and an action g, I can think of them as recipes, because I can combine them via f >>= g. It's only after I combine all of my actions together that I apply the result to my input (via "run").
Well, that's just like function composition. In particular, if I have a function f, and a function g, I can think of them as recipes, because I can combine them via f . g.
First a nitpick: At the beginning of the thread I had pointed out how co/monadic co/bind generalizes function /application/, i.e. flip ($). Generalized function /composition/ on the other hand has a different type. For instance, in the case of monads it's \begin{code} (<.>) :: Monad m => (a -> m b) -> (c -> m a) -> (c -> m b) (<.>) f g c = (g c) >>= f \end{code} Function (<.>) is flip (>>>) in the instance of Monad m => Arrow (Kleisli m). (For a moment there I couldn't find it in the haskell libs. Would be nice if Hoogle could read instances such as these. I must not be using Hoogle right, I couldn't even locate (>>=) by type signature.) Returning to the main point, like you and Dan P, I also have my reservations explaining a monadified value as a recipe, although for arguably different reasons. It's too chef-centric for me, to continue with the original analogy. I have an allergic reaction to "run" functions, at least what they connote. I claim that in genuinely monadic programming, you never think about "run". Code that's genuinely monadic works for all monads. Code like that is what you want to write. Or put another way, you just program like before except lifting stuff into an arbitrary monad. You then write different monads to retrofit the various add-on computations you want performed. I thought this is well-known for over 15 years? -- View this message in context: http://www.nabble.com/Explaining-monads-tf4244948.html#a12185261 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.