On 5/31/07, Stefan Holdermans
Dan,
If you want to enforce associativity just create your own Eq instance and make it a pattern there.
Could you elaborate on that? It's still early here and I've had only one cup of of coffee yet.
Cheers,
Stefan
QuickCheck allows you to approximately verify properties by testing them on randomly generated input. The stated properties thus cannot formally be proved, but they act as a pretty good formal specification. (Full automatic theorem proving for a language as expressive as Haskell is impossible or infeasible. So we have to approximate.) prop_assocJoin x y z = join x (join y z) == join (join x y) z -- or, more generally associative :: (Eq a) => (a -> a -> a) -> a -> a -> a -> Bool associative f x y z = f x (f y z) == f (f x y) z prop_assocJoin = associative join -- to check this for a given implementation of "join", you need to: import Test.QuickCheck Main> quickCheck prop_assocJoin This also requires that QC can generate arbitrary values of type "e". See the QuickCheck documentation for more infos on that: http://www.cs.chalmers.se/~rjmh/QuickCheck/manual.html / Thomas -- "Remember! Everytime you say 'Web 2.0' God kills a startup!" - userfriendly.org, Jul 31, 2006