Comonad documentation

[justinhj]

Added a document page for Comonads

[codecov-io]

Codecov Report

Merging #2888 into master will not change coverage.
The diff coverage is n/a.

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  Lines        6949    6949           
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  Hits         6546    6546           
  Misses        403     403

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[LukaJCB]

This is cool, thanks! I'm happy to accept this as is, but I also feel a practical example would go a long way :)

[justinhj]

I’ll spend some time finding a good example. I see Runar has posted a lot about Comonads so there are his implementations of Conways game of life as well as a graph traversal but maybe that is a bit big for this context.

[justinhj]

I've made the suggested corrections. I gave some thought to a motivating example. Perhaps it would be good to write a doc page for Store, the dual of State, and include an example of how that is useful, then link to it from the comonad page later.

[kailuowang]

Thanks!