Is there any way to determine, at the level of grammar, that the order of expressions does not matter?

[kafkiansky]

A simple case: I have a set of blocks, the order of which is not important. In example

WHITESPACE = _{ " " | "\t" | "\r" | "\n" }
a = {"a"}
b = {"b"}

I want the user to be able to write both a b and b a, with both a and b being required, but their order is not important. The workaround is:

or = { (a ~ b) | (b ~ a) }

But I have too many blocks for which describing such a thing would be difficult.

[phoenixr-codes]

This would be possible with a PEEK_ANY keyword.

From my understanding PEEK_ALL matches the first item in the stack, then the second, ….

So it probably would make sense to invent a PEEK_ANY keyword?

A solution with this could look like this:

blocks = {
    "a"
  | "b"
  | "c"
  | "d"
}

main = {
  PUSH(blocks)
  ~ (
    !PEEK_ANY
    ~ PUSH(blocks)
  ){3}
}

After all I think the workaround is the only solution that works for this case now.