compile.js

compile.js

var clone = function (o) {
        // return a copy of o.
        // http://stackoverflow.com/questions/728360/copying-an-object-in-javascript
        if(null === o || 'object' !== typeof o) {
            return o;
        }

        var copy = o.constructor();

        for(var attr in o) {
            if(o.hasOwnProperty(attr)) {
                copy[attr] = o[attr];
            }
        }

        return copy;
    },
    compile = function (musexpr) {
        // convert a MUS 'AST' to a NOTE program
        var endTime = function (start, musexpr) {
            // return the end time of a MUS program
            // given the start time
            switch(musexpr.tag) {
                case 'note':
                case 'rest':
                    return start + musexpr.dur;

                case 'seq':
                    return endTime(start, musexpr.left) + endTime(start, musexpr.right);

                case 'par':
                    return Math.max(endTime(start, musexpr.left), endTime(start, musexpr.right));

                case 'section':
                    return endTime(musexpr.section);

                default:
                    // wtf?
            }
        },
        convertPitch = function (pitch) {
            // convert scientific notation to midi numbers for pitches
            var pitchLetter = pitch[0].toLowerCase(),
                octave = parseInt(pitch[1], 10),
                conversion = {
                    'c': 0,
                    'd': 2,
                    'e': 4,
                    'f': 5,
                    'g': 7,
                    'a': 9,
                    'b': 11
                };

            return 12 + 12 * octave + conversion[pitchLetter];
        },
        compile = function (musexpr, start) {
            // compile a MUS expression starting at start
            if(musexpr.tag === 'note' || musexpr.tag === 'rest') {
                // do not modify original muse expression
                musexpr = clone(musexpr);

                if(musexpr.tag === 'note') {
                    musexpr.pitch = convertPitch(musexpr.pitch);
                }

                musexpr.start = start;
                return [musexpr];
            }

            else if(musexpr.tag === 'repeat') {
                var notes = compile(musexpr.section, start),
                    duration = endTime(0, musexpr.section),
                    res = [];

                for(var i = 0; i < musexpr.count; ++i) {
                    res = res.concat(notes);

                    // fix start times
                    for(var j = 0, l = notes.length; j < l; ++j) {
                        var note = notes[j],
                            newNote = clone(note);

                        newNote.start += duration;
                        notes[j] = newNote;
                    }
                }

                return res;
            }

            // seq or par
            var left = compile(musexpr.left, start),
                rightStart = musexpr.tag === 'seq' ? endTime(start, musexpr.left) : start,
                right = compile(musexpr.right, rightStart);

            return left.concat(right);
        };

    return compile(musexpr, 0);
};