[Haskell-cafe] Fundep Curiosity
rendel at cs.au.dk
Tue May 12 10:33:53 EDT 2009
Christopher Lane Hinson wrote:
> I've noticed that a large majority of fundeps I see in other people's
> libraries are written:
> class C a b | b -> a
> Where the dependent parameter appears first in the MPTC. Is there a
> reason for this?
> AFAIK, there isn't any semantic significance to the order of parameters
> in an MPTC. Why do many haskellers find this configuration more intuitive?
The order of parameters in an MPTC is significant if you want to use
newtype deriving, which can only be used with the last parameter, by
explicitly providing all other parameters.
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