On Fri, Jan 16, 2009 at 12:00:40PM -0500, David Menendez wrote:
A reference to the writer monad and to Data.Foldable might be helpful. So far as I know they are the only uses of the Monoid abstraction in the standard libraries.
It's probably a good idea to explicitly state the three monoid laws.
I've added the laws.
It would be nice to explain what operations have been chosen for the Monoid instances of Prelude data types. (Maybe this belongs in the Prelude documentation.)
The right place for that is the instances, as soon as Haddock starts showing instance comments (http://trac.haskell.org/haddock/ticket/29). Then this information will be listed under both the type and the class.
I'd add a reminder that if you're defining a type with a Monoid instance, your documentation should explain what the instance does.
When that Haddock enhancement is done, this will be general advice for instances of all classes.