Proposal #3339: Add (+>) as a synonym for mappend
conor at strictlypositive.org
Sat Jul 18 10:17:00 EDT 2009
On 18 Jul 2009, at 14:23, Edward Kmett wrote:
> Yeah, the Monoid instance for Maybe is somewhat unfortunate.
> I can see where they were going as Maybe does provide the natural
> extension of a semigroup into a monoid by adding a unit element, but
> it doesn't have a Semigroup class to build on, and so has to require
> Monoid and in the end you get a definition that conflicts with the
> MonadPlus/Alternative instances for Maybe, and only really helps if
> you have broken Monoid instances around that are secretly just
Types should mean more than mere data representations. The
current Monoid instance is inconsistent with the broad
interpretation of Maybe as a monad for exceptional computations.
An isomorphic data representation can and should be used to
attach a unit element to a semigroup,
Data structures are data with structure.
All the best
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