The first good implementation I'm aware of is Egil Möller's from 2003 (https://srfi.schemers.org/srfi-49/srfi-49.html). My independently researched prediction in 2017 was that no one will ever discover a place where parens or other visible syntax is needed. That sets up an easy proof by contradiction (and I've built a database of over 10k languages so far, looking for a single scenario where you would need them, and haven't found one yet). Here are 19 demo languages covering lots of scenarios demonstrating utility without parens (https://github.com/treenotation/jtree/tree/master/langs). A glaring hole though, now that I think about it, is that I don't have a good Lisp-like Tree Language. I think a Bel Tree Language would be an excellent example project (and I'm happy to assist anyone who wants to make an attempt, and if no one has the bandwidth and it's not done by next year perhaps I'll find the time to give it a go).

> They are the structure that supports Lisp's simplicity and consistency, which is what all the good things come from.

I agree with this, but would say they are "one" structure, not "the", and that there are other options (I have one idea in tree notation, but not ruling out that there are more, perhaps better ones).

> If you take them out, it gets complicated and isn't worth it.

I agree with this, but think there is a future tipping point related to tooling. Tree Notation was quite terrible 2 years ago, but now with type checking, syntax highlighting, autocomplete, I hate to use Lisp and other languages (everything feels unfinished, because I know the syntax characters can be removed).

I think we'll hit a tipping point where the tooling for Lisp without parens is good enough that the benefits of dropping them make dropping them a no-brainer. Could I be wrong? Sure, it's a forecast/prediction. But I want to encourage people to invent new alternatives, to try everything under the sun, and not to settle that they are somehow needed. We can make it better.

Any such tooling tipping point would likely make the syntax of the underlying representation irrelevant. What to view the logic in tree notation? Or how about with the parens? Or the parens, but so faint you can't see them? Or collapsing aspects of the code you're not currently concerned with? What gets eventually transformed into the 1s and 0s executed by the machine, and its various representations along the way are really not the concern of the person writing at the top of that stack, at least not most of the time.

Personally I find the added vertical space by tree notation very distracting and that it breaks the scan of my reading. But that's my personal preference, and something that could be addressed with tooling. And that's the point: same thing can be said with the parens of lisp or other editing/IDE tooling.

I happen to like fine-tipped pens, while others enjoy the smoothness of thicker rollerballs. Is one better than another? Do the benefits of one make using it to the exclusion of others a no-brainer? Does my enjoyment of fine-tipped pens preclude others from developing new pen types or new writing implementations all together? Might my evangelism for fine-tipped pens turn people off from exploring the perfection that is the Uni-ball Signo UM-151 0.28mm (in blue-black ink, of course)?

To each their own. Find the medium that best helps you express your message. And that may not be the same for others. And that's okay.

> Is one better than another?

Rollerballs and fine-tipped pens are probably equivalent, on an order of magnitude scale. However, surely we can agree that both are far superior to feather or dipped pens?

I am forecasting the difference between parens free Lisp and status quo Lisp will resemble the chasm between dip pens and fountain pens.

Lots of Lispers say, "dip pens are fine! After a while you don't even notice you are dipping them." Whereas I see a future where a lot more can get done easier because we don't have to waste time dipping our pens.