[Haskell-cafe] Representing Hierarchies with Typeclasses

[Dimitri DeFigueiredo]

I have looked at how to embedded object oriented systems into haskell
for practical reasons.
By far the best resource I found was Oleg Kiselyov and Ralph Lämmel's work:

https://arxiv.org/pdf/cs/0509027.pdf

It shows the multiple possibilities.
I have used the idea of having a super class be a polymorphic type with
a tail.

data Point s = Pt { x :: Int, y:: Int, tail :: s}

And then specializing the parameter s into your derived class

type Radius = Int
type Circle = Point Radius

many times.

But *be warned*, I try to avoid object hierarchies like the plague! They
lead to code that is not reusable.
You may want to consider other simpler possibilities. Here is one of my
earlier experiments that may be useful to you (I no longer have the
views expressed there).

https://github.com/dimitri-xyz/inheritance-in-haskell

Cheers,

Dimitri

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