[Haskell-cafe] class-instance

[Patrick Browne]

A functional dependency seems to allow me to express my rather strange
requirement.

class Person i n | i  -> n where
     pid :: i
     name :: i -> n

instance Person Int String where
     pid = 1
     name(1) = "john"


-- name(pid::Int) will produce john

Thanks for your help

Pat



On 17/01/2011 14:07, Patrick Browne wrote:
> On 17/01/2011 13:04, Ketil Malde wrote:
>>> So other PERSONs would have different types, say:
> 
> I think the problem is there is just one constant p1 in the class and
> there needs to be multiple constants in the implementation (one for each
> person). It seems difficult to specify this using type classes So, some
> data declaration as you suggest will probably be needed.
> 
> Thanks,
> Pat
> 
> 
> 
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