[Haskell-cafe] FDs [The container problem]

Andrew Coppin andrewcoppin at btinternet.com
Sat Sep 27 14:43:28 EDT 2008

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 That helps...

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

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