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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