[Haskell-cafe] monad constraint + record update

[Henning Thielemann]

Brent Yorgey schrieb:
> On Mon, Dec 22, 2008 at 06:19:07PM +0100, Peter Padawitz wrote:
>> I'd like to define a monad Set for types in the class Eq. But how can the 
>> arguments of Set be constrained when Set is defined as an instance of 
>> Monad? instance Eq a => Monad Set where ... obviously cannot work.
>>
>> Is there a standard update function for fields in data types, something 
>> that OO programmers do with assignments like obj.attr := value ?
>>
>> Peter
>>
> 
> Note there is already a package on Hackage to do exactly this, rmonad.
> 
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rmonad

And also
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-accessor