The append example is meant to make a general point about the connection between dependent types and Haskell with extensions.
I know that the example itself is rather trivial, and DML/index types, Omega, Haskell+GAD and Chameleon might seem as too big canons for a rather small target. > Second you can express append in a much simpler and readable > way in Haskell using type classes: > > ------------------------------------------------------------- > > data Nil deriving Show > data List a = Cons a (List a) deriving Show > > class Append l l' l'' | l l' -> l'' where > append :: l -> l' -> l'' > instance List l' => Append Nil l' l' where > append _ l' = l' > instance Append l l' l'' => Append (Cons a l) l' (Cons a l'') where > append (Cons a l) l' = Cons a (append l l') > > ------------------------------------------------------------- > > Thats the complete definition, no need for extra stuff or > complex exqualities or casts... > > Doesn't look too bad to me. > Good, I was waiting for some type class trickery :) You turn clauses into instance declarations. This will only work for terminating programs! Martin _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
