add xen!

repl/src/evaluate.ts

@@ -3,6 +3,7 @@ import './tone';
 import './midi';
 import './voicings';
 import './tonal.mjs';
+import './xen.mjs';
 import shapeshifter from './shapeshifter';
 import { minify } from './parse';
 import * as Tone from 'tone';

repl/src/xen.mjs

@@ -0,0 +1,37 @@
+import { Pattern } from '../../strudel.mjs';
+import { mod } from '../../util.mjs';
+
+function edo(name) {
+  if (!/^[1-9]+edo$/.test(name)) {
+    throw new Error('not an edo scale: "' + name + '"');
+  }
+  const [_, divisions] = name.match(/^([1-9]+)edo$/);
+  return Array.from({ length: divisions }, (_, i) => Math.pow(2, i / divisions));
+}
+
+function getXenScale(scale, indices) {
+  if (typeof scale === 'string') {
+    if (/^[1-9]+edo$/.test(scale)) {
+      return edo(scale);
+    }
+    throw new Error('unknown scale name: "' + scale + '"');
+  }
+  if (!indices) {
+    return scale;
+  }
+  return scale.filter((_, i) => indices.includes(i));
+}
+
+function xenOffset(xenScale, offset, index = 0) {
+  const i = mod(index + offset, xenScale.length);
+  const oct = Math.floor(offset / xenScale.length);
+  return xenScale[i] * 440 * Math.pow(2, oct);
+}
+
+Pattern.prototype._xen = function (scaleNameOrRatios) {
+  return this._asNumber()._withEvent((event) => {
+    const frequency = xenOffset(getXenScale(scaleNameOrRatios), event.value);
+    return event.withValue(() => frequency).setContext({ ...event.context, type: 'frequency' });
+  });
+};
+Pattern.prototype.define('xen', (scale, pat) => pat.xen(scale), { composable: true, patternified: true });