[Haskell-cafe] monad constraint + record update

[Peter Padawitz]

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