>>> I suggest going with Unicode terminology and conventional predicates:
>>> ascii-open-punctuation?, ascii-close-punctuation?, and
>>> ascii-mirroring-character. Not quite as terse, perhaps, but more
> I believe they are only more familiar to Unicode experts :) "Bracket" is
> almost universal slang, even known by laypeople, for any kind of
> parenthetical symbol with an opposite pair. And the only mirroring
> punctuation in the ASCII range are the four kinds of brackets. "Bracket"
> is also a shorter and less abstract word than "punctuation".
> However, "mirroring-bracket" is just as good as "opposing-bracket", so I
> can change it without further ado. It's only one character longer too.
> "Opening" and "closing" are words of the same length so I preferred them
> even though "open" and "close" are shorter. No strong opinion here.
Will you have open-punctuation?, close-punctuation? and
mirroring-character? procedures in R7RS-large by some names?