Give special treatment to the last interval in keepUnique

ref #341

src/parser/__tests__/expression.spec.ts

@@ -2133,6 +2133,11 @@ describe('SonicWeave expression evaluator', () => {
     const {fraction} = parseSingle('2 -1');
     expect(fraction).toBe('1');
   });
+
+  it('keeps unique strings', () => {
+    const strings = evaluate('keepUnique(["hello", "world", "hello"])');
+    expect(strings).toEqual(['hello', 'world']);
+  });
 });
 
 describe('Poor grammar / Fun with "<"', () => {
@@ -2170,6 +2175,7 @@ describe('Poor grammar / Fun with "<"', () => {
     expect(fraction).toBe('9');
   });
 
+  // TODO: Move under the correct heading.
   it('multiplies a monzo from the left', () => {
     const {fraction} = parseSingle('2 [2 -1>');
     expect(fraction).toBe('16/9');

src/parser/__tests__/stdlib.spec.ts

@@ -1594,4 +1594,9 @@ describe('SonicWeave standard library', () => {
       '2/1',
     ]);
   });
+
+  it('preserves equave formatting in organize()', () => {
+    const scale = expand('1;2/1;organize()');
+    expect(scale).toEqual(['2/1']);
+  });
 });

src/stdlib/builtin.ts

@@ -1947,7 +1947,16 @@ function keepUnique(this: ExpressionVisitor, scale?: SonicWeaveValue) {
   if (!Array.isArray(scale)) {
     throw new Error('An array is required.');
   }
+  if (!scale.length) {
+    return [];
+  }
   const seen = new Set();
+  const equave = scale.pop()!;
+  if (equave instanceof Interval) {
+    seen.add(equave.valueOf());
+  } else {
+    scale.push(equave);
+  }
   const result: SonicWeavePrimitive[] = [];
   for (const interval of scale) {
     const value = interval ? interval.valueOf() : interval;
@@ -1957,6 +1966,9 @@ function keepUnique(this: ExpressionVisitor, scale?: SonicWeaveValue) {
     result.push(interval);
     seen.add(value);
   }
+  if (equave instanceof Interval) {
+    result.push(equave);
+  }
   return result;
 }
 keepUnique.__doc__ =