Re: [Haskell-cafe] monad constraint + record update

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 -Brent