Perhaps having unary minus (and especially unary plus) is just a bad idea in general; just mandate "0 - expr". To make negative constants work properly, you still have to either special case literals "256", "65536", etc. and ideally check whether they got negated or not, or introduce a special syntax just for them, like "~1" of ML for negative one, or "-1" (which you are not allowed to break with whitespace) of some other language I've forgotten the name of.

While we're at it, probably the unary bitwise complement could go as well? Obviously, "^(0-1)" would suck to write but since 99% of the time bitwise "not" used in expressions/statements like "expr &~ mask..." or "var &= ~mask", I feel like simply having binary "and-not" operator that looks like "&~" or "&^" (Golang) is just better.

Also, a small prize (a "thank you!" from a stranger on the Internet i.e. me) to someone who can propose a good syntax for compound assignment with reversed subtraction:

    x ^= 0-1    # in-place bitwise complement
    x ^= true   # in-place logical negation
    x ?= 0      # in-place integer negation???

> Also, a small prize (a "thank you!" from a stranger on the Internet i.e. me) to someone who can propose a good syntax for compound assignment with reversed subtraction:

I would do away with operator-assign operators and instead introduce a general syntax for updating a variable that can be used with any expression.

  x = _ + 1  # increment x
  x = 0 - _  # negate x
  output = sanitizeHtml(_)
  index = (_ + 1) % len(arr)

+1 on the convenience of a "mask" operator that perform the and-not. It's an operation that's used more often than others which do have the privilege of having their own symbol, like xor.