[Haskell-cafe] Re: Newbie question
Brent Yorgey
byorgey at gmail.com
Mon Jan 21 12:33:54 EST 2008
2008/1/21 Alexander Seliverstov <seliverstov.a at gmail.com>:
> So, the function type "(Num a)=>Integer->a" means that return value of
> this function can be cast to any particular instance of class Num.
>
> Ok. I have a my own class "class A a" and want to write function like
> this "f:: (A a)=>Integer->a". Can I do it?
>
>
Only if you make the function f a member of class A. Then it is the
responsibility of each particular type which is an instance of A to define a
way of converting an Integer into a value of that type. For example:
class A a where
f :: Integer -> a
... other functions...
instance A Integer where
f = id
instance A String where
f = show
and so on.
-Brent
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