GraphQL is a really elegant way of querying a datastore, instead of REST or SQL. Eg https://waywardmonkeys.org/2016/03/15/graphql-beyond-the-web/ (querying OS metadata example)
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Go has an elegant approach to defining example functions, which are shown in docs as `main()` with the output: https://go.dev/blog/examples
Bril is a cute intermediate language for teaching (think simplified LLVM IR): https://www.cs.cornell.edu/~asampson/blog/bril.html
The idea of providing a standard JSON format to help students write basic passes is really elegant.
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.