Hi,
On 9/18/07, Benjamin Franksen
Ashley Yakeley wrote:
Conor McBride wrote:
My usual rule of thumb is that inherent natural monoidal structure should have a higher priority than just applicative lifting of monoidal structure from the value type.
Monoid is a bit ridiculous as a class, as there are frequently several useful monoids on a type, leading to a collection of ugly wrapper newtypes.
Monoid ought to be a type, in my view. And each of those wrapper classes can be replaced by a value in that type.
Would you care to elaborate this idea? Do you mean a record with two functions?
Here is how you can do that: data Monoid a = Monoid { mempty :: a, mappend :: a -> a -> a } int_add :: Monoid Int int_add = Monoid { mempty = 0, mappend = (+) } int_mul :: Monoid Int int_mul = Monoid { mempty = 1, mappend = (*) } -- etc... -Iavor