Not sure what you mean by "Why are you trying to write C code in Haskell?"
Please explain. This whole exercise is my attempt to translate *The
Littler MLer* and its last chapter where they go into functors. The authors
are old Scheme men. Maybe that's the problem?
On Mon, Apr 5, 2021 at 6:53 AM Anthony Clayden
Or am I barking up the completely wrong tree here, i.e., this isn't a functor issue?
Yes you are barking up the wrong tree/no this isn't a Functor issue.
create just one generic plus that would handle both the plus :: Int -> Int -> Int and the plus2 :: MyNum -> MyNum -> MyNum.
A Functor would need to be of the form of a parameterised type. That is, the `f` in `f a`. Neither `Int` nor `MyNum` are parameterised.
You want a plus-like method that's polymorphic/generic across different Peano-like numeric representations. IOW you want an overloading. That's what typeclasses are for:
class PolyPlus a where polyPlus :: a -> a -> a
instance PolyPlus Int where polyPlus = plus
instance PolyPlus MyNum where polyPlus = plus2
(In those instances you could just put the definitions for those functions/no need to define them separately. BTW both those definitions are truly horrible non-idiomatic Haskell. Why are you trying to write C code in Haskell?)
AntC
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