'Elm Lens' is a really neat idea: it exposes the number of callers to the current function in your editor!
miniblog.
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Nifty example of a Haskell lens library using custom type errors to explain what's wrong:
https://github.com/mrkgnao/silica/blob/master/README.md
Skimming the docs for lens.js: https://www.npmjs.com/package/safety-lens makes lenses look rather like lisp's setf to me. Is this superficial or deep?