Personal tools

Talk:What a Monad is not

From HaskellWiki

Revision as of 23:44, 23 November 2009 by Ashley Y (Talk | contribs)

Jump to: navigation, search

1 Nicolas Pouillard Comments

I disagree with: "So ordering is not in any way essential to what a monad is."

There is commutative monads, great! Other than that the order is important. Moreover there is nothing wrong to see >>= as a sequencing operator.

I also disagree the "IO is impure" paragraph: Indeed only IO will trigger visible side effects, but this is only due to the common evaluation of IO primitives. Moreover I would say that only the runtime system is impure because it does reduce 'main :: IO ()', other than that we are just building a computation plan in a pure way.

Although I agree that the common issue is too mix monad and impurity, and the impurity question is only releated to IO.

2 "Monads are not values"

Yes they are! But they are not of the type of their arguments. For instance "return 3" is a value that has (or can have) type "IO Int". But it is not a value of type Int. —Ashley Y 23:44, 23 November 2009 (UTC)