Neat. Lots of good stuff.

What's the interplay between infix notation and operator precedence? Expressions are not infix?

Also, please explain the dictionary and set duality.

FWIW, in my toy language, I use one syntax for sets, lists, and arrays, delimited with brackets '[' and ']'. Whereas maps, dicts, and (prototypical) objects use curlys '{' and '}'. A la JavaScript et al.

Lastly, wrt using '++' for concatenating lists, there have been times I've wanted sugar for prepending to a list. So maybe support both 'atom ++ list' and 'list ++ atom'?

For future updates, please us posted.