On Thu, 29 May 2003 22:48:05 -0500 "Tim Sweeney" <[EMAIL PROTECTED]> wrote:
> If it's not possible to implement a typesafe RefMonad instance > directly in Haskell, without making use of built-in imperative > features like IO, then doesn't this refute the claims that monads > implement imperative features functionally? > > -Tim You certainly can have an instance of RefMonad that -simulates- updateable references. You can't implement this with update inplace without an update inplace primitive and if Haskell had an update inplace primitive that you could use anywhere it wouldn't be a pure language. Monads in Haskell -allow- imperative features and use of imperative features without breaking the purity of the entire language. Outside a monadic computation equational reasoning always holds, even when talking about imperative actions. That monads implement an imperative effect doesn't mean they implement it the same way an imperative language would. Of course, the actual implementation doesn't matter so implementing it imperatively is just as good as implementing it functionally as far as static semantics go, which is why everything (IO&ST) works out. _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
