Great post on how to use union types effectively: https://robots.thoughtbot.com/modeling-with-union-types (has a lovely example of modelling a deck of cards: how do you handle suits and jokers?)
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Steve Jobs famously asked for smooth scrolling (i.e. not line-by-line) in a Smalltalk demonstration and they changed the UI live.
Here's a lovely 2 minute YouTube video demonstrating that modification: https://www.youtube.com/watch?v=eEz08IlcNMg
Git repositories have the lovely properties that deletes aren't propagated. Shared/cloud storage sync deletes across devices.
Accidentally deleting content in a local git repo, and even pushing it, is a safe operation.
Lovely example of using fuel to debug compiler optimisation passes in GHC: