[Haskell-cafe] Re: Verbosity of imperative code

[Scherrer, Chad]

> On Tue, Dec 06, 2005 at 10:58:45PM +0300, Bulat Ziganshin wrote:
> > the third-priority problem is language itself. in particular, i hate
> > Haskell school of imperative manipulations:
> > 
> > x' <- readIORef x
> > y' <- readIORef y
> > writeIORef z (x'*y')

Here's a way to make some of this less messy:

class PlusEq a b m | a -> m where
    (+=) :: a -> b -> m ()

instance (Num a) => PlusEq (IORef a) a IO where
    xRef += y = do x <- readIORef xRef
                   writeIORef xRef (x + y)

instance (Num a) => PlusEq (IORef a) (IORef a) IO where
    xRef += yRef = do y <- readIORef yRef
                      xRef += y

Then instead of 

do x <- xRef
   y <- yRef
   writeIORef yRef (x + y)

you can just say y += x. I've started on an InPlace module to do things
like this in general.

-Chad Scherrer