On Fri, 2009-01-16 at 14:16 +0100, david48 wrote:
Upon reading this thread, I asked myself : what's a monoid ? I had no idea. I read some posts, then google "haskell monoid".
The first link leads me to Data.Monoid which starts with
<< Description The Monoid class with various general-purpose instances.
Inspired by the paper /Functional Programming with Overloading and Higher-Order Polymorphism/, Mark P Jones (http://citeseer.ist.psu.edu/jones95functional.html) Advanced School of Functional Programming, 1995.
Ross just updated the documentation for the Monoid module. Here is how it reads now: The module header now reads simply: A class for monoids (types with an associative binary operation that has an identity) with various general-purpose instances. Note, no links to papers. And the Monoid class has: The class of monoids (types with an associative binary operation that has an identity). The method names refer to the monoid of lists, but there are many other instances. Minimal complete definition: 'mempty' and 'mappend'. Some types can be viewed as a monoid in more than one way, e.g. both addition and multiplication on numbers. In such cases we often define @newtype@s and make those instances of 'Monoid', e.g. 'Sum' and 'Product'. If you or anyone else has further concrete suggestions / improvements then post them here now! :-) Duncan