[Haskell-cafe] Data.Tree.Zipper in the standard libraries

[Krasimir Angelov]

That is annoying. I remember that there were people arguing that Monad
should be used instead of Maybe but I don't remember the reasons.
Personaly I feel quite happy with Maybe and I am using it in my own
code. There should be a consistent approach in the different libraries
or at least in a single package like "containers".

While googling for Zipper I also found this article:

http://citeseer.ist.psu.edu/hinze01web.html

Is this better alternative to Zipper? Have someone better experience with it?

Regards,
  Krasimir



On 5/23/08, Jules Bean <jules at jellybean.co.uk> wrote:
> Krasimir Angelov wrote:
> > The monads design is used in Data.Map i.e.
> >
> > lookup :: (Monad m, Ord k) => k -> Map k a -> m a
> >
>
> which is widely considered a poor design decision and a wart on Data.Map.
>
> :-)
>
> Seriously, if you don't return a useful error message, then Maybe is as good
> as it gets, why not use it?
>
> (And there really is only one kind of error possible here, in each case)
>
> 'fail' only adds information in the case it has a useful error message (in
> which case I'd encourage MonadError m =>)
>
> Jules
>