MUS compiler exercises

js/music/music.js

@@ -0,0 +1,100 @@
+var TONE_POS_FOR_NOTE = {
+    C: 0,
+    "C#": 1, "Db": 1,
+    D: 2,
+    "D#": 3, "Eb": 3,
+    "E": 4,
+    "F": 5,
+    "F#": 6, "Gb": 6,
+    "G": 7,
+    "G#": 8, "Ab": 8,
+    "A": 9,
+    "A#": 10, "Bb": 10,
+    "B": 11
+}
+var OCTAVE_LENGTH = 12;
+var MIDI_BASE = 12;
+
+var getMidiNo = function(note) {
+    note = note.toUpperCase();
+    var i = note.length - 1;
+    var octave = parseInt(note.charAt(i));
+    var pos = TONE_POS_FOR_NOTE[note.substr(0, i)];
+    return (OCTAVE_LENGTH * octave) + MIDI_BASE + pos;
+};
+
+var endTime = function (time, expr) {
+    if (expr.tag === 'note' || expr.tag === 'rest') {
+        return time + expr.dur;
+    }
+    if (expr.tag === 'seq') {
+        return endTime(endTime(time, expr.left), expr.right);
+    }
+    if (expr.tag === 'par') {
+        return Math.max(endTime(time, expr.left), endTime(time, expr.right));
+    }
+    if (expr.tag === 'repeat') {
+        return time + (expr.count * endTime(0, expr.section));
+    }
+    throw 'Unhandled tag: ' + expr.tag;
+
+};
+
+var getNotes = function(startTime, me) {
+    var startOfRight;
+    if (me.tag === 'note') {
+        return [{
+            tag: 'note',
+            pitch: getMidiNo(me.pitch),
+            start: startTime,
+            dur: me.dur
+        }];
+    }
+    if (me.tag === 'rest') {
+        return [{
+            tag: 'rest', start: startTime, dur: me.dur
+        }];
+    }
+    if (me.tag === 'seq') {
+        startOfRight = endTime(startTime, me.left);
+        return getNotes(startTime, me.left)
+                .concat(getNotes(startOfRight, me.right));
+    }
+    if (me.tag === 'par') {
+        return getNotes(startTime, me.left)
+                .concat(getNotes(startTime, me.right));
+    }
+    if (me.tag === 'repeat') {
+        var notes = [];
+        var nextStart = startTime;
+        for (var i = me.count; i > 0; i--) {
+            notes = notes.concat(getNotes(nextStart, me.section));
+            nextStart = endTime(nextStart, me.section);
+        }
+        return notes;
+    }
+    throw "Unhandled tag: " + me.tag;
+};
+
+var compile = function (musexpr) {
+    var startTime = 0;
+    return getNotes(startTime, musexpr);
+};
+
+var melody_mus = 
+    { tag: 'seq',
+      left: { tag: 'repeat',
+         section: { tag: 'seq',
+            left: { tag: 'note', pitch: 'a4', dur: 250 },
+            right: { tag: 'note', pitch: 'b4', dur: 250 } },
+         count: 3
+      },
+      right:
+       { tag: 'seq',
+         left: { tag: 'rest', dur: 250 },
+         right: { tag: 'seq',
+           left: { tag: 'note', pitch: 'c4', dur: 500 },
+           right: { tag: 'note', pitch: 'd4', dur: 500 } } } };
+
+console.log(melody_mus);
+console.log(compile(melody_mus));