Fix chunk, add fastChunk and repeatCycles (#712)

* Match behaviour of chunk with tidal, add fastChunk for old strudel behaviour. Also adds repeatCycles. fixes #689

* documentation

packages/core/pattern.mjs

@@ -2100,23 +2100,43 @@ export const { iterBack, iterback } = register(['iterBack', 'iterback'], functio
   return _iter(times, pat, true);
 });
 
+/**
+ * Repeats each cycle the given number of times.
+ * @name repeatCycles
+ * @memberof Pattern
+ * @returns Pattern
+ * @example
+ * note(irand(12).add(34)).segment(4).repeatCycles(2).s("gm_acoustic_guitar_nylon")
+ */
+const _repeatCycles = function (n, pat) {
+  return slowcat(...Array(n).fill(pat));
+};
+
+const { repeatCycles } = register('repeatCycles', _repeatCycles);
+
 /**
  * Divides a pattern into a given number of parts, then cycles through those parts in turn, applying the given function to each part in turn (one part per cycle).
  * @name chunk
+ * @synonyms slowChunk, slowchunk
  * @memberof Pattern
  * @returns Pattern
  * @example
  * "0 1 2 3".chunk(4, x=>x.add(7)).scale('A minor').note()
  */
-const _chunk = function (n, func, pat, back = false) {
+const _chunk = function (n, func, pat, back = false, fast = false) {
   const binary = Array(n - 1).fill(false);
   binary.unshift(true);
-  const binary_pat = _iter(n, sequence(...binary), back);
+  // Invert the 'back' because we want to shift the pattern forwards,
+  // and so time backwards
+  const binary_pat = _iter(n, sequence(...binary), !back);
+  if (!fast) {
+    pat = pat.repeatCycles(n);
+  }
   return pat.when(binary_pat, func);
 };
 
-export const chunk = register('chunk', function (n, func, pat) {
-  return _chunk(n, func, pat, false);
+const { chunk, slowchunk, slowChunk } = register(['chunk', 'slowchunk', 'slowChunk'], function (n, func, pat) {
+  return _chunk(n, func, pat, false, false);
 });
 
 /**
@@ -2132,6 +2152,21 @@ export const { chunkBack, chunkback } = register(['chunkBack', 'chunkback'], fun
   return _chunk(n, func, pat, true);
 });
 
+/**
+ * Like `chunk`, but the cycles of the source pattern aren't repeated
+ * for each set of chunks.
+ * @name fastChunk
+ * @synonyms fastchunk
+ * @memberof Pattern
+ * @returns Pattern
+ * @example
+ * "<0 8> 1 2 3 4 5 6 7".fastChunk(4, x => x.color('red')).slow(4).scale("C2:major").note()
+  .s("folkharp")
+ */
+const { fastchunk, fastChunk } = register(['fastchunk', 'fastChunk'], function (n, func, pat) {
+  return _chunk(n, func, pat, false, true);
+});
+
 // TODO - redefine elsewhere in terms of mask
 export const bypass = register('bypass', function (on, pat) {
   on = Boolean(parseInt(on));

packages/core/test/pattern.test.mjs

@@ -1003,4 +1003,23 @@ describe('Pattern', () => {
       );
     });
   });
+  describe('chunk', () => {
+    it('Processes each cycle of the source pattern multiple times, once for each chunk', () => {
+      expect(sequence(0, 1, 2, 3).slow(2).chunk(2, add(10)).fast(4).firstCycleValues).toStrictEqual([
+        10, 1, 0, 11, 12, 3, 2, 13,
+      ]);
+    });
+  });
+  describe('fastChunk', () => {
+    it('Unlike chunk, cycles of the source pattern proceed cycle-by-cycle', () => {
+      expect(sequence(0, 1, 2, 3).slow(2).fastChunk(2, add(10)).fast(4).firstCycleValues).toStrictEqual([
+        10, 1, 2, 13, 10, 1, 2, 13,
+      ]);
+    });
+  });
+  describe('repeatCycles', () => {
+    it('Repeats each cycle of the source pattern the given number of times', () => {
+      expect(slowcat(0, 1).repeatCycles(2).fast(6).firstCycleValues).toStrictEqual([0, 0, 1, 1, 0, 0]);
+    });
+  });
 });

test/__snapshots__/examples.test.mjs.snap

@@ -1115,27 +1115,6 @@ exports[`runs examples > example "chop" example index 0 1`] = `
 `;
 
 exports[`runs examples > example "chunk" example index 0 1`] = `
-[
-  "[ 0/1 → 1/4 | note:A4 ]",
-  "[ 1/4 → 1/2 | note:B3 ]",
-  "[ 1/2 → 3/4 | note:C4 ]",
-  "[ 3/4 → 1/1 | note:D4 ]",
-  "[ 1/1 → 5/4 | note:A3 ]",
-  "[ 5/4 → 3/2 | note:B3 ]",
-  "[ 3/2 → 7/4 | note:C4 ]",
-  "[ 7/4 → 2/1 | note:D5 ]",
-  "[ 2/1 → 9/4 | note:A3 ]",
-  "[ 9/4 → 5/2 | note:B3 ]",
-  "[ 5/2 → 11/4 | note:C5 ]",
-  "[ 11/4 → 3/1 | note:D4 ]",
-  "[ 3/1 → 13/4 | note:A3 ]",
-  "[ 13/4 → 7/2 | note:B4 ]",
-  "[ 7/2 → 15/4 | note:C4 ]",
-  "[ 15/4 → 4/1 | note:D4 ]",
-]
-`;
-
-exports[`runs examples > example "chunkBack" example index 0 1`] = `
 [
   "[ 0/1 → 1/4 | note:A4 ]",
   "[ 1/4 → 1/2 | note:B3 ]",
@@ -1156,6 +1135,27 @@ exports[`runs examples > example "chunkBack" example index 0 1`] = `
 ]
 `;
 
+exports[`runs examples > example "chunkBack" example index 0 1`] = `
+[
+  "[ 0/1 → 1/4 | note:A4 ]",
+  "[ 1/4 → 1/2 | note:B3 ]",
+  "[ 1/2 → 3/4 | note:C4 ]",
+  "[ 3/4 → 1/1 | note:D4 ]",
+  "[ 1/1 → 5/4 | note:A3 ]",
+  "[ 5/4 → 3/2 | note:B3 ]",
+  "[ 3/2 → 7/4 | note:C4 ]",
+  "[ 7/4 → 2/1 | note:D5 ]",
+  "[ 2/1 → 9/4 | note:A3 ]",
+  "[ 9/4 → 5/2 | note:B3 ]",
+  "[ 5/2 → 11/4 | note:C5 ]",
+  "[ 11/4 → 3/1 | note:D4 ]",
+  "[ 3/1 → 13/4 | note:A3 ]",
+  "[ 13/4 → 7/2 | note:B4 ]",
+  "[ 7/2 → 15/4 | note:C4 ]",
+  "[ 15/4 → 4/1 | note:D4 ]",
+]
+`;
+
 exports[`runs examples > example "clip" example index 0 1`] = `
 [
   "[ 0/1 → 1/4 | note:c s:piano clip:0.5 ]",
@@ -1857,6 +1857,19 @@ exports[`runs examples > example "fast" example index 0 1`] = `
 ]
 `;
 
+exports[`runs examples > example "fastChunk" example index 0 1`] = `
+[
+  "[ 0/1 → 1/2 | note:C2 s:folkharp ]",
+  "[ 1/2 → 1/1 | note:D2 s:folkharp ]",
+  "[ 1/1 → 3/2 | note:E2 s:folkharp ]",
+  "[ 3/2 → 2/1 | note:F2 s:folkharp ]",
+  "[ 2/1 → 5/2 | note:G2 s:folkharp ]",
+  "[ 5/2 → 3/1 | note:A2 s:folkharp ]",
+  "[ 3/1 → 7/2 | note:B2 s:folkharp ]",
+  "[ 7/2 → 4/1 | note:C3 s:folkharp ]",
+]
+`;
+
 exports[`runs examples > example "fastGap" example index 0 1`] = `
 [
   "[ 0/1 → 1/4 | s:bd ]",
@@ -3646,6 +3659,27 @@ exports[`runs examples > example "release" example index 0 1`] = `
 ]
 `;
 
+exports[`runs examples > example "repeatCycles" example index 0 1`] = `
+[
+  "[ 0/1 → 1/4 | note:42 s:gm_acoustic_guitar_nylon ]",
+  "[ 1/4 → 1/2 | note:38 s:gm_acoustic_guitar_nylon ]",
+  "[ 1/2 → 3/4 | note:35 s:gm_acoustic_guitar_nylon ]",
+  "[ 3/4 → 1/1 | note:38 s:gm_acoustic_guitar_nylon ]",
+  "[ 1/1 → 5/4 | note:42 s:gm_acoustic_guitar_nylon ]",
+  "[ 5/4 → 3/2 | note:38 s:gm_acoustic_guitar_nylon ]",
+  "[ 3/2 → 7/4 | note:35 s:gm_acoustic_guitar_nylon ]",
+  "[ 7/4 → 2/1 | note:38 s:gm_acoustic_guitar_nylon ]",
+  "[ 2/1 → 9/4 | note:42 s:gm_acoustic_guitar_nylon ]",
+  "[ 9/4 → 5/2 | note:36 s:gm_acoustic_guitar_nylon ]",
+  "[ 5/2 → 11/4 | note:39 s:gm_acoustic_guitar_nylon ]",
+  "[ 11/4 → 3/1 | note:41 s:gm_acoustic_guitar_nylon ]",
+  "[ 3/1 → 13/4 | note:42 s:gm_acoustic_guitar_nylon ]",
+  "[ 13/4 → 7/2 | note:36 s:gm_acoustic_guitar_nylon ]",
+  "[ 7/2 → 15/4 | note:39 s:gm_acoustic_guitar_nylon ]",
+  "[ 15/4 → 4/1 | note:41 s:gm_acoustic_guitar_nylon ]",
+]
+`;
+
 exports[`runs examples > example "reset" example index 0 1`] = `
 [
   "[ 0/1 → 1/4 | s:hh ]",