Hello Claus, Monday, March 6, 2006, 2:35:04 PM, you wrote:
also, while i like dynamic records for some types of tasks, i think that the "spirit" of Haskell in whole is to give explicit definitions of all types used and in this respect this type extension in not on "main way".
CR> record extension is the basis for record concatenation, which is CR> the basis for composing programs that use records. for instance, CR> if you have two attribute grammars that compute two sets of CR> attributes and you want to compose them into a single grammar, CR> you run into troubles. (dual arguments for extensible variants, CR> be it for exception types, or for extensible grammars that cover CR> haskell+extensions without having to specify and maintain two CR> separate grammars). and the concept of partial type specifications CR> is not uncommon in Haskell (polymorphism, type classes). (sorry for late answer) this again should be maintained in "Haskell way", i.e. with static type declarations: data Pizza = ... data Cola = ... type PizzaWithCola = Pizza+Cola weight :: PizzaWithCola -> Double weight pc = pizzaWeight pc + colaWeight pc pizzaWeight :: Pizza -> Double colaWeight :: Cola -> Double it is one more remainder of what we need OOP-like features such as data fields inheritance. O'Haskell has something in this area, although afair it doesn't support the multiple inheritance -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com