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exercism fetch haskell pov

POV

Reparent a graph on a selected node.

Tree Reparenting

This exercise is all about re-orientating a graph to see things from a different point of view. For example family trees are usually presented from the ancestor's perspective:

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5
    +------0------+
    |      |      |
  +-1-+  +-2-+  +-3-+
  |   |  |   |  |   |
  4   5  6   7  8   9

But the same information can be presented from the perspective of any other node in the graph, by pulling it up to the root and dragging its relationships along with it. So the same graph from 6's perspective would look like:

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9
        6
        |
  +-----2-----+
  |           |
  7     +-----0-----+
        |           |
      +-1-+       +-3-+
      |   |       |   |
      4   5       8   9

This lets us more simply describe the paths between two nodes. So for example the path from 6-9 (which in the first graph goes up to the root and then down to a different leaf node) can be seen to follow the path 6-2-0-3-9

This exercise involves taking an input graph and re-orientating it from the point of view of one of the nodes.

Getting Started

For installation and learning resources, refer to the exercism help page.

Running the tests

To run the test suite, execute the following command:

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stack test

If you get an error message like this...

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No .cabal file found in directory

You are probably running an old stack version and need to upgrade it.

Otherwise, if you get an error message like this...

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No compiler found, expected minor version match with...
Try running "stack setup" to install the correct GHC...

Just do as it says and it will download and install the correct compiler version:

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stack setup

Running GHCi

If you want to play with your solution in GHCi, just run the command:

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stack ghci

Feedback, Issues, Pull Requests

The exercism/haskell repository on GitHub is the home for all of the Haskell exercises.

If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue. We'll do our best to help you!

Source

Adaptation of exercise from 4clojure https://www.4clojure.com/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.