[Haskell-cafe] FDs [The container problem]

[Andrew Coppin]

Bulat Ziganshin wrote:
> Hello Andrew,
>
> Saturday, September 27, 2008, 9:23:47 PM, you wrote:
>
>   
>> Can anybody actually demonstrate concretely how FDs and/or ATs would
>> solve this problem? (I.e., enable you to write a class that any 
>> container can be a member of, despite constraints on the element types.)
>>     
>
> you may find comprehensive explanation in ghc user manual, it's
> chapter about FDs use this as motivating example :)
>   

Section 8.6.2, "Functional Dependencies": "There should be more 
documentation, but there isn't (yet). Yell if you need it."

Yeah, that's real helpful. :-P But hey, there's an academic paper... *sigh*

Ooo, wait a sec, section 8.6.2.2. That helps...

Mmm, OK. Now can somebody explain the "FDs cause problems" part?