On Mon, 11 Oct 1999, Adrian Hey wrote:
> On Mon 11 Oct, Lars Lundgren wrote:
> > I'm sure a lot of poeple have gotten this wrong. I would be surprised if
> > not all the experienced haskellers has this view though.
>
> Probably so, but this view seems in complete contradiction to
> that of the Clean world. So I'm still confused :-)
>
I just took a glance at Clean. (Glanced through "The Ins and Outs of Clean
I/O" by Peter Achten and Rinus Plasmeijer.) I think their solution with
unique types is really neat.
One downside may be that they have made the type system more complex
since it has to handle all the uniqness tags.
They deal with side effects (IO) by tagging the values with * and calling
them unique. Haskell deals with side effects (IO) by using an abstract
data type IO a which denotes an action [with clean type *World ->
(a,*World) ]. In both cases, the compiler is notified that it is not ok to
change order of evaluation.
In the Related work section, they mention Monadic IO and writes "To our
knowledge combining monads of different type is a rather tedious task..."
I'm reluctant to say that I agree. I have written a few programs using
monad transformers and while everything works in principle, it is, well -
tedious...
I also do not like the tendency to put more things in the IO monad (I'm
thinking about the extensions with IORef). I like stToIO better, but
somehow it still feels like a hack. Maybe some library support for monad
transformers and maybe even some syntactig sugar would do the trick.
They also wrote "[The monadic IO approach] over determines order of
evaluation". I'm a bit puzzled about that statement. Is it true? Comments
anyone?
/Lars L
