Thanks for the feedback! Tree Calculus is a calculus/logic, see Specification page or the book by Barry Jay (linked on that page) for way way better and detailed verbose explanations. It only defines what I chose to call "t" on the website, Barry uses "Δ" in his book and papers.
So without anything else, we'd have to talk about programs in terms of "(t t) t ..." or binary trees, which gets unwieldy quickly. The first natural step, for practical purposes, is to allow definitions "foo = ...", then some syntactic sugar for lists, functions, etc. Ooops and now we have a "language". If you open the "Playground" page there's a summary of what exactly is TC and what is syntactic sugar (and really nothing more!) on top of it.
I like to think that the line is so blurry precisely because TC needs nothing but a bit of syntactic sugar to feel like a usable PL haha.
Right, it's a programming language the way the lambda calculus or pi calculus or whatever are programming languages—I did understand that much!
I love the idea of having a website like this to introduce people to one of the less popular calculi, and the playground is a great touch. It might be helpful to have an introductory paragraph that explains exactly what the tree calculus is, starting from what a "calculus" is—your target audience seems to be people who aren't otherwise going to go out of their way to read Barry's papers, which means you can't assume as much background as you currently do. As a reference, I'm a casual PL nerd who actually has read academic papers related to some of the less well-known calculi with an eye towards implementing them, so I'm on the more informed end of the spectrum of your target audience.
Have you considered making this site open source? No pressure if not, but if so I'd be happy to contribute to polishing up the landing page. I'm very interested in learning more about this anyway, and I'm more than willing to help!
So without anything else, we'd have to talk about programs in terms of "(t t) t ..." or binary trees, which gets unwieldy quickly. The first natural step, for practical purposes, is to allow definitions "foo = ...", then some syntactic sugar for lists, functions, etc. Ooops and now we have a "language". If you open the "Playground" page there's a summary of what exactly is TC and what is syntactic sugar (and really nothing more!) on top of it.
I like to think that the line is so blurry precisely because TC needs nothing but a bit of syntactic sugar to feel like a usable PL haha.