2009/12/29 Alexander Solla <a...@2piix.com>: > Every Monad defines a "join" and "eval" function in terms of > bind and return, and the Monad type class does this for you. > You can use "join" to construct queries against a monad, and > eval to "run" a monad, like a state machine. (Conceptually, > the Haskell runtime calls the IO monad's "specially defined" > eval method on "Main.main". This is the only Haskell monad > whose eval function is not defined in terms of >>= and return, > as far as I know.)
Maybe I am misunderstanding you, but `eval :: M t -> t' does not fall out of the definition of a monad. You need more than monadicity -- you need an algebra for `M' at `t'. -- Jason Dusek _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
