Roman chord notation in Strudel, including secondary chords

strudel-roman-chords-extended.js

const romanNumerals = ['i', 'ii', 'iii', 'iv', 'v', 'vi', 'vii'];
function romanToIndex(s) {
  for (let index = romanNumerals.length - 1; index >= 0; index--) {
    const numeral = romanNumerals[index];
    if (s.startsWith(numeral)) {
      return { index, isMinor: true, suffix: s.substring(numeral.length) };
    } else if (s.startsWith(numeral.toUpperCase())) {
      return { index, isMinor: false, suffix: s.substring(numeral.length) };
    }
  }
}
register('roman', function (scaleName, pat) {
  return pat.as("roman1:roman2").fmap(({ roman1, roman2 }) => {
    let targetScale = scaleName;
    if (roman2) {
      const { index, isMinor } = romanToIndex(roman2);
      targetScale = n(index).scale(scaleName).fmap(({ note }) => note + ':' + (isMinor ? 'minor' : 'major'));
    }
    const { index, isMinor, suffix } = romanToIndex(roman1);
    return n(index).scale(targetScale).fmap(({ note }) => {
      return note.slice(0, -1) + (isMinor ? 'm' : '') + suffix;
    });
  }).outerJoin();
});

strudel-roman-chords-extended.md

Usage:

"<I7 [ii7:V V7:V] V7 [ii7 V7]>"
  .roman("d:major")
  .chord()
  .voicing()
  .sound("piano")