Brian Hulley wrote:
Bulat Ziganshin wrote:
[Apologies for replying to a reply of a reply but I don't seem to have received the original post]
I've been thinking along these lines too, because it has always seemed to me that laziness is just a real nuisance because it hides a lot of inefficiency under the carpet as well as making the time/space behaviour of programs difficult to understand...
One question is how to get some kind of "do" notation that would work well in a strict setting. The existing "do" notation makes use of lazyness in so far as the second arg of >> is only evaluated when needed. Perhaps a new keyword such as "go" could be used to use >>= instead ie:
go {e1;e2;e3} === e1 >>= (\_-> (e2 >>= (\_->e3)))
Of course this doesn't solve the problem of how to translate programs that make heavy use of mapM etc.
I wonder: is monadic programming really dependent on lazyness or is there a realistic (ie not impossibly complicated) way to use monads in a strict setting?
A related question is: could monadic programming ever be as efficient as side-effect programming?
Regards, Brian. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
What about writing functions in a modified form of Control.Monad.Identity that ensures the return value that forces the return values:
module Control.Monad.Strict (Weak,mkWeak,unsafeMkWeak,runWeak, Deep,mkDeep,unsafeMkDeep,runDeep) where
Weak uses seq to achieve WHNF for it's argument
newtype Weak a = WeakCon {runWeak :: a} mkWeak x = seq x (WeakCon x) unsafeMkWeak x = WeakCon x
instance Functor Weak where fmap f w = mkWeak (f (runWeak w))
instance Monad Weak where return x = mkWeak x w >>= f = f (runWeak w)
I can't make the deepSeq version typecheck: Deep uses deepSeq to evaluate it's argument
newtype Deep a = DeepCon {runDeep :: a} mkDeep x = deepSeq x (DeepCon a) unsafeDeep x = DeepCon x
instance Functor Deep where fmap f d = mkDeep (f (runDeep d))
instance Monad Deep where return d = mkDeep d d >>= f = f (runDeep d)