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A 30 line javascript spreadsheet is similar for me to when I first saw Norvig's 21 line python spelling corrector ( http://norvig.com/spell-correct.html ): this language is more powerful and expressive than I thought. I'm increasingly believing that HTML/CSS/JS in a browser is a viable common runtime. This demo does quite a lot to solidify that belief.
The only things that are powerful and expressive in JavaScript are bastardized beyond recognition versions of ideas from Lisp, Smalltalk and Self. You get those dynamic mechanisms that we know for 50 years now (lambda expressions and runtime method dispatch, oh wow) to be useful but without learning any lessons learned in those 50 years about how to design a coherent language based on those concepts, you just get a h…
Sadly, I can't really run python in the browser.