Sources:
- https://github.com/purescript/purescript-functors/
- https://github.com/paf31/purescript-pairing/
- https://github.com/paf31/purescript-day/
- https://marcinszamotulski.me/posts/finite-state-machines.html
- https://personal.cis.strath.ac.uk/conor.mcbride/Kleisli.pdf
- https://github.com/freebroccolo/purescript-ends/
- http://comonad.com/reader/2008/zapping-strong-adjunctions/