Reading about the nonempty list type in Haskell: https://wiki.haskell.org/Non-empty_list (example of the 'enforce everything in the type system' philosophy)
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Which programming languages follow the "cathedral" design philosophy, where they provide most of: the runtime, stdlib, debugger, LSP, test harness, code formatter and package manager?
Go, Dart and Smalltalk are the closest I can think of.
I've built a simple personal wiki/blog at https://notes.wilfred.me.uk/. It has few features and little content, but it works.
I've tried to apply an agile philosophy: ship it ASAP. This is hard for side projects. I found the features I wanted after shipping changed considerably!
An elegant example of the Pharo philosophy: extending the UI/debug tools to give custom visualisations of objects within your project: