On Sat, 2008-02-02 at 12:33 -0500, Denis Bueno wrote: > Is it possible to use the ST monad as a (drop-in) replacement for the > State monad in the following situation? If not, is there a "best > practice" for refactoring? > > I have a bunch of functions that return state actions: > > type MyState = ... > > foo1 :: T1 -> State MyState a > foo2 :: T2 -> State MyState a > ... > foon :: Tn -> State MyState a > > And I'd like to refactor this to use the ST monad, mechanically, if > possible. All uses of the MyState inside State are single-threaded. > > In my application, MyState is a record with 5 or so fields. One of > those fields uses a list to keep track of some information, and I'd > like to change that to STUArray, because it changes my bottleneck > operations from O(n) to O(1). This, of course, requires having the ST > monad around, in order to achieve the proper time complexity. > > Is there an easy way to do this? In the future, should I *start out* > with the ST monad if I suspect I'll need to use an imperative data > structure for efficiency reasons? I started out with State because > I'm modeling a transition system, so it seemed natural. > > Any advice is appreciated.
%s/State MyState/MyMonad s/g type MyState s = ... s ... type MyMonad s = StateT (MyState s) (ST s) _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
