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

Brandon S. Allbery KF8NH allbery at ece.cmu.edu
Fri May 23 13:36:04 EDT 2008

On 2008 May 23, at 13:34, Luke Palmer wrote:

> On Fri, May 23, 2008 at 10:55 AM, 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.
> It is?  Can you point to somewhere explaining that?  I rather liked  
> that idiom.

I'd argue that the poor design decision was killing MonadZero, and the  
type of Data.Map.lookup is a hackaround.

brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH

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