[Haskell-cafe] Type Directed Name Resolution

[Miguel Mitrofanov]

11.11.2010 16:53, Stephen Tetley пишет:
> On 11 November 2010 13:10, Lauri Alanko<la at iki.fi>  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
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