Hi, I'm not sure if this is possible but I am trying to use Haskell’s type class to specify *model expansion*. Model expansion allows the specification of new symbols (known as enrichment) or the specification further properties that should hold on old symbols. I am trying to enrich simplified Monoids to Groups. The code below is not intended to do anything other than to specify simplified Groups as a subclass of Monoid. The main problem is that I cannot use ! on the LHS of equations in Group. Is it possible to expand the specification of Monoid to Group using Haskell type classes? Pat data M = M deriving Show -- Monoid with one operation (!) and identity e (no associativity) class Monoid a where (!) :: a -> a -> a e :: a a ! e = a -- A Group is a Monoid with an inverse, every Group is a Monoid -- (a necessary condition in logic: Group implies Monoid) -- The inverse property could be expressed as: -- 1) forAll a thereExists b such that a ! b = e -- 2) (inv a) ! a = e class Monoid a => Group a where inverse :: a -> a -- Haskell does not like ! on the LHS of equation for inverse in Group. -- (inverse a) ! a = e This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie