TIL XEmacs has more datatypes! For example, a keymap is an opaque type rather than a list: https://emacs.stackexchange.com/a/2472
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Really cute approach to reporting type errors: when there's a type error, show an example of a runtime error that the type check has prevented!
Data-Driven Techniques for Type Error Diagnosis https://escholarship.org/uc/item/59s4h4pv
Playing with optional type signatures in Python, I realise that the return type is the most important to me.
I'd much rather have a function with only a return type instead of a function with only parameter types. It's often quick to add too.
The most common selling point I hear for Nix is having a list of all the packages you need.
On a traditional Linux distro, I just install things and forget about them. A curated, commented list would certainly be handy when I have a new system.