focus tweak for squeezeJoin - another go at fixing #216 (#221)

Fixes squeezeJoin, and in the process struct/keepif. fixes #216

Co-authored-by: Felix Roos <flix91@gmail.com>

packages/core/pattern.mjs

@@ -649,12 +649,22 @@ export class Pattern {
   // pattern of values. In this case it takes whole cycles of the inner pattern to fit each event
   // in the outer pattern.
   _squeezeJoin() {
+    // A pattern of patterns, which we call the 'outer' pattern, with patterns
+    // as values which we call the 'inner' patterns.
     const pat_of_pats = this;
     function query(state) {
+      // Get the events with the inner patterns. Ignore continuous events (without 'wholes')
       const haps = pat_of_pats.discreteOnly().query(state);
+      // A function to map over the events from the outer pattern.
       function flatHap(outerHap) {
-        const pat = outerHap.value._focusSpan(outerHap.wholeOrPart());
-        const innerHaps = pat.query(state.setSpan(outerHap.part));
+        // Get the inner pattern, slowed and shifted so that the 'whole'
+        // timespan of the outer event corresponds to the first cycle of the
+        // inner event
+        const inner_pat = outerHap.value._focusSpan(outerHap.wholeOrPart());
+        // Get the inner events, from the timespan of the outer event's part
+        const innerHaps = inner_pat.query(state.setSpan(outerHap.part));
+        // A function to map over the inner events, to combine them with the
+        // outer event
         function munge(outer, inner) {
           let whole = undefined;
           if (inner.whole && outer.whole) {
@@ -753,7 +763,7 @@ export class Pattern {
   // Similar to compress, but doesn't leave gaps, and the 'focus' can be
   // bigger than a cycle
   _focus(b, e) {
-    return this._fast(Fraction(1).div(e.sub(b))).late(b);
+    return this._fast(Fraction(1).div(e.sub(b))).late(b.cyclePos());
   }
     
   _focusSpan(span) {
@@ -1347,11 +1357,16 @@ function _composeOp(a, b, func) {
           pat = preprocess(pat);
           other = preprocess(other);
         }
-        var result = pat['_op' + how](other, (a) => (b) => _composeOp(a, b, op));
+        var result;
         // hack to remove undefs when doing 'keepif'
         if (what === 'keepif') {
+          // avoid union, as we want to throw away the value of 'b' completely
+          result = pat['_op' + how](other, (a) => (b) => op(a, b));
           result = result._removeUndefineds();
         }
+        else {
+          result = pat['_op' + how](other, (a) => (b) => _composeOp(a, b, op));
+        }
         return result;
       };
       if (how === 'Squeeze') {

packages/core/test/pattern.test.mjs

@@ -42,6 +42,7 @@ import {
   id,
   ply,
   rev,
+  time,
 } from '../index.mjs';
 
 import { steady } from '../signal.mjs';
@@ -791,6 +792,13 @@ describe('Pattern', () => {
         ).firstCycle(),
       );
     });
+    it('Squeezes to the correct cycle', () => {
+      expect(
+        pure(time.struct(true))._squeezeJoin().queryArc(3,4).map(x => x.value)
+      ).toStrictEqual(
+        [Fraction(3.5)]
+      )
+    });
   });
   describe('ply', () => {
     it('Can ply(3)', () => {