Added Satellite exercise

[tofische]

Added a new Haskell practice exercise Satellite based on the available problem specification.

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[MatthijsBlom]

@ErikSchierboom I am not familiar with this feature, so I cannot judge this.

[ErikSchierboom]

Topics are deprecated and are not used by the website. They are allowed to be in the config.json as they used to be used and they could be useful to help determine the practices and prerequisites fields.

[MatthijsBlom]

Hmm. This exercise is about binary trees, but Data.Tree.Tree is a rose tree. Should we be more precise and use some dedicated BinaryTree type instead?

[tofische]

Hmm. This exercise is about binary trees, but Data.Tree.Tree is a rose tree. Should we be more precise and use some dedicated BinaryTree type instead?

I agree with you, but I couldn't find a ready-to-use binary tree in any common package. I didn't want to use some exotic package, and I also didn't want to let the students to create their own tree implementation.

The closest I could find is https://hackage.haskell.org/package/tree-traversals-0.1.2.0/docs/Data-BinaryTree.html - what do you think about the usage of this package?

[ErikSchierboom]

I agree with you, but I couldn't find a ready-to-use binary tree in any common package. I didn't want to use some exotic package, and I also didn't want to let the students to create their own tree implementation.

It is possible to pre-define the tree type in a separate file and include it in the files.editor key in the .meta/config.json file. That way, the file is downloaded when using the CLI and shown as read-only when using the online editor.

[MatthijsBlom]

Neat!

If we add a pre-defined type in this way we should probably add a note about it in instructions.append.md.

-- Which type to choose?

data BinaryTree a = Leaf   | Node a (BinaryTree a) (BinaryTree a)
-- or
data BinaryTree a = Leaf a | Node a (BinaryTree a) (BinaryTree a)

[tofische]

Neat!

If we add a pre-defined type in this way we should probably add a note about it in instructions.append.md.

-- Which type to choose?

data BinaryTree a = Leaf   | Node a (BinaryTree a) (BinaryTree a)
-- or
data BinaryTree a = Leaf a | Node a (BinaryTree a) (BinaryTree a)

I have to admit that I'm not keen on the idea of providing a custom-made basic data structure - one of the purposes of the exercises is to point people towards suitable existing libraries. At least for me it was a big benefit that I got from the Exercism, so I don't want to withhold it from others.

What are the arguments against using Data.BinaryTree?

[MatthijsBlom]

What are the arguments against using Data.BinaryTree?

To me: that it is not small. Many rose trees are not binary trees. Haskell allows and encourages expressing one's intent precisely. Defining new types even for single use is not unusual.

[tofische]

What are the arguments against using Data.BinaryTree?

To me: that it is not small. Many rose trees are not binary trees. Haskell allows and encourages expressing one's intent precisely. Defining new types even for single use is not unusual.

Are we talking about the same thing? Source of Data.BinaryTree:

data BinaryTree a = Leaf | Branch (BinaryTree a) a (BinaryTree a)
  deriving (Show, Functor, Eq)

[MatthijsBlom]

No, sorry. I thought we were talking about Data.Tree from containers.

tree-traversals seems not a commonly used package. In any case it would have to be added to the test runner. I have no definite opinion on whether we should use it.

[tofische]

No, sorry. I thought we were talking about Data.Tree from containers.

tree-traversals seems not a commonly used package. In any case it would have to be added to the test runner. I have no definite opinion on whether we should use it.

This is a valid argument.

[ErikSchierboom]

tree-traversals seems not a commonly used package. In any case it would have to be added to the test runner. I have no definite opinion on whether we should use it.

When possible, we'd prefer not to add libraries to the test runner.

one of the purposes of the exercises is to point people towards suitable existing libraries

I'd argue that this isn't generally true, although it can be in individual cases. Our idea is that students solve things without using libraries, as Exercism is all about teaching fluency in a language, but not necessarily everything that goes with it (like tooling and libraries).

[ErikSchierboom]

LGTM!

[ErikSchierboom]

Topics are deprecated and are not used by the website. They are allowed to be in the config.json as they used to be used and they could be useful to help determine the practices and prerequisites fields.