Re: [Haskell-cafe] Type Directed Name Resolution

11.11.2010 16:53, Stephen Tetley пишет:

On 11 November 2010 13:10, Lauri Alanko wrote:

...

{-# LANGUAGE EmptyDataDecls, MultiParamTypeClasses, FunctionalDependencies #-}

data PetOwner data FurnitureOwner

data Cat = Cat { catOwner :: PetOwner } data Chair = Chair { chairOwner :: FurnitureOwner }

class Owned a b | a -> b where owner :: a -> b

instance Owned Cat PetOwner where owner = catOwner

instance Owned Chair FurnitureOwner where owner = chairOwner

This is fairly onerous for people who are programming to an outside schema (i.e. a relational database) as it leads to boiler plate along two axes - data type definitions plus class definitions for accessors.

I don't like the details current TDNR proposal, but if improved records are never going to happen, TDNR has benefit for this situation.

That's kinda the point, it can work the other way: ugly solution like TDNR can prevent improved records from ever appearing.

Incidentally there is now a member of the ML family with a sophisticated record system - MLPolyR: http://ttic.uchicago.edu/~wchae/wiki/pmwiki.php _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe