[Haskell-beginners] Long time no Haskell....simple typeclass question

[Nicholls, Mark]

This is the basic problem...

I have a data type, that has some functions that require typeclass constraints (this example doesn't...but that's not the point).

I have a typeclass, and I want to declare my datatype inhabits that type class....

> data Func a b = Func (a->b)

> exeFunc :: (Ord a) => Func a b -> a -> b
> exeFunc (Func g) = g

> class IFunc f where
>   exe :: f a b -> a -> b

> instance IFunc Func where
>   exe = exeFunc

Follow your nose and obviously

"No instance for (Ord a) arising from a use of 'exeFunc'"

But how do I constain "a" in the instance declaration, when "a" doesn't even appear

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