Add support for re-assignment using arrays of indices

src/parser/__tests__/stdlib.spec.ts

@@ -1356,4 +1356,20 @@ describe('SonicWeave standard library', () => {
     `);
     expect(major).toEqual(['9/8', '5/4', '4/3', '3/2', '5/3', '15/8', '2/1']);
   });
+
+  it('parses Rage Todi (golfed)', () => {
+    const scale = expand(`
+      rank2(3/2 white, 1, 5, 2/1 white)
+      $[[2, 5]] *~= 135/128 black
+    `);
+    expect(scale).toEqual([
+      '256/243 white',
+      '32/27 white',
+      '45/32 black',
+      '3/2 white',
+      '128/81 white',
+      '15/8 black',
+      '2/1 white',
+    ]);
+  });
 });

src/parser/statement.ts

@@ -465,6 +465,32 @@ export class StatementVisitor {
       }
       if (Array.isArray(object)) {
         const index = subVisitor.visit(node.name.key);
+        if (Array.isArray(index)) {
+          if (!Array.isArray(value)) {
+            throw new Error('Unrecoverable error in array assignment.');
+          }
+          let j = 0;
+          for (let i = 0; i < index.length; ++i) {
+            const idx = index[i];
+            if (!(typeof idx === 'boolean' || idx instanceof Interval)) {
+              throw new Error(
+                'Only booleans and intervals can be used as indices.'
+              );
+            }
+            if (idx === true) {
+              object[i] = value[j++];
+              continue;
+            } else if (idx === false) {
+              continue;
+            }
+            let k = idx.toInteger();
+            if (k < 0) {
+              k += object.length;
+            }
+            object[k] = value[j++];
+          }
+          return undefined;
+        }
         if (!(index instanceof Interval)) {
           throw new Error('Array access with a non-integer.');
         }