Documentation for the Invariant typeclass

[markus1189]

Adds a tut section about Invariant as discussed in #164. I oriented the explanation according to @ceedubs example, I hope this is okay.

I wasn't able to test the jekyll serve because it fails on my pc due to a missing ruby dependency, so I am not sure if adding the file is enough to make it show up on the typeclasses site? If someone could check that that'd be great :).

If merged this fixes #164.

-- 24pullrequests

[codecov-io]

Current coverage is 85.06%

Merging #710 into master will increase coverage by +0.05% as of 6174f09

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  Files          162     162       
  Stmts         2229    2229       
  Branches        74      74       
  Methods          0       0       
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+ Hit           1895    1896     +1
  Partial          0       0       
+ Missed         334     333     -1

Review entire Coverage Diff as of 6174f09

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[ceedubs]

Thanks! Looks good at a first glance. I'll take a more detailed look.

[ceedubs]

We should probably be careful with wording here. In Cats, Functor means covariant functor. To me, this sentence makes it sound like Invariant is a subtype of Functor, while it's actually the other way around. This may be solved by just changing Functor to a generic "functor". That could potentially also be confusing to people who think that Functor and "functor" would be synonymous. It may be fine though.

[markus1189]

Added a full example at the end ;)

[ceedubs]

In the spirit of the work that has just been done for #709, maybe we should put all but the last line of this into a tut:silent shed, and just use tut (with output) for the today |+| timeLeft. The output for imports, etc is pretty noisy.

[markus1189]

I added two versions of the import, the version that imports all the stuff and a commented out version that is more explicit. @mikejcurry good catch for the typo :)

[ceedubs]

I ran jekyll serve locally and the Invariant type class auto-populated in the links and looks good. 👍 thanks!

[adelbertc]

👍