On Jan 15, 2009, at 1:21 PM, David Menendez wrote:
On Thu, Jan 15, 2009 at 11:46 AM, Ross Mellgren
wrote: Second is that there appears to be no way to document an _instance_. It would be really handy if there were even a single line under "Instances > Monoid ([] a)" that explained how the type class was implemented for the list type. As it is, if you know what a Monoid is already, it's easy to figure out how it would be implemented.
Not necessarily. Any instance of MonadPlus (or Alternative) has at least two reasonable Monoid instances: (mplus, mzero) and (liftM2 mappend, return mempty). [] uses the first and Maybe uses the second.
Sorry my brain apparently misfired writing the original email. What I meant to say is that for the Monoid instance on [a] it's fairly easy (knowing what a Monoid is) to figure out how it's implemented, but that's not true for other classes or instances. That is to say, I agree with you, and intended to up front ;-) -Ross