Graphic composition using painters algorithm can be seen as a monoid. data Graphic = Empty | Graphic `Over` Graphic | Ellipse Bounds | .... instance Monoid Graphic where mempty = Empty mappend = Over So all functions that operate on monoids can be used on Graphic as well, like mconcat that converts a [Graphic] into a Graphic On Thu, Jan 15, 2009 at 9:51 PM, Don Stewart <dons@galois.com> wrote:
duncan.coutts:
On Thu, 2009-01-15 at 19:46 +0000, Andrew Coppin wrote:
PS. As a small aside... Is the Monoid class actually used *anywhere* in all of Haskell?
Yes.
They're used quite a lot in Cabal. Package databases are monoids. Configuration files are monoids. Command line flags and sets of command line flags are monoids. Package build information is a monoid.
It is also used in the Foldable class which is a nice interface for traversing/visiting structures. Binary serialisation is also a monoid.
Also, xmonad configuration hooks are monoidal. So all those xmonad users gluing together keybindings are using the Monoid class.
-- Don _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe