add the author's implementation for future reference

ccppjava · ccppjava · commit f83f319167cc · 2012-04-26T11:32:04.000+01:00
diff --git a/nathansununiversity_02_author.js b/nathansununiversity_02_author.js
@@ -0,0 +1,44 @@
+var endTime = function (time, expr) {
+    if (expr.tag === 'note') return time + expr.dur;
+    if (expr.tag === 'seq')
+        return endTime(endTime(time, expr.left), expr.right);
+    return Math.max(endTime(time, expr.left), endTime(time, expr.right));
+};
+
+var compileT = function (musexpr, time) {
+    if (musexpr.tag === 'note') {
+        return [ { tag: 'note',
+                  pitch: musexpr.pitch,
+                  start: time,
+                  dur: musexpr.dur } ];
+    }
+    if (musexpr.tag === 'seq') {
+        var left = compileT(musexpr.left, time);
+        var ldur = endTime(time, musexpr.left);
+        var right = compileT(musexpr.right, ldur);
+        return left.concat(right);
+    }
+    if (musexpr.tag === 'par') {
+        var left = compileT(musexpr.left, time);
+        var right = compileT(musexpr.right, time);
+        return left.concat(right);
+    }
+};
+
+var compile = function (musexpr) {
+    return compileT(musexpr, 0);
+};
+
+var melody_mus =
+    { tag: 'seq',
+      left:
+       { tag: 'par',
+         left: { tag: 'note', pitch: 'c3', dur: 250 },
+         right: { tag: 'note', pitch: 'g4', dur: 500 } },
+      right:
+       { tag: 'par',
+         left: { tag: 'note', pitch: 'd3', dur: 500 },
+         right: { tag: 'note', pitch: 'f4', dur: 250 } } };
+
+console.log(melody_mus);
+console.log(compile(melody_mus));
