Ch 7 - Review tree show instance and solutions

[razcore-rad]

The exercise is:

1. (Easy) Write Eq and Show instances for the following binary tree data structure:

data Tree a = Leaf | Branch (Tree a) a (Tree a)

The solution is implemented using generics. By this point derive isn't discussed not to mention generics. There's discussion to include at least derive in Ch6 #149, but not generics. Thus the solutions should be "manual" solutions.

Also the implementation of the show instance is pretty subjective so the reader needs a bit more details on how the solution should look like otherwise he's forced to look at the test suite. Including an output example would do the trick, something like: (Branch (Branch Leaf 5 Leaf) 4 (Branch Leaf 6 Leaf)) or something like that maybe.

[milesfrain]

I'll make a PR to fix this.

I'm thinking of including a hint that this can be done with generic (along with a link to the guide) to make this optionally more interesting, since this exercise is really just a repeat of content from the previous chapter. The generic solution will be shown commented-out next to the hand-written solution.

I agree about the ambiguity of show output, but I think this is straightforward to correct by just looking at the test output in the terminal (so no need to dig through the test suite). A downside of making a note is that it's more material that needs to be kept in sync.

[razcore-rad]

Yeah I see what you mean, but the problem is that if the exercise is ambiguous to begin with and you first have to "fail" to get it right, as a beginner that's not a great experience. I think this should be solved with a hint of the expected output still.

Say you correctly implement the show instance, but it isn't acceptable because it doesn't match perfectly with the test suite. As a beginner you really start wondering where you went wrong instead and doubt yourself. Maybe it's just me, but I start questioning if I screwed up instead of realizing "oh yea, it's cause the test is just for an arbitrary implementation".

I guess what I'm saying is the first thing you notice is the failed status, not why the failure happened and that's just not good beginner experience.

[milesfrain]

@razcore-art, let me know what you think of #235