function ls() {
	var options;
	var gopts;
	var clbk;
	var opts;
	var dir;
	var err;

	opts = copy( defaults );
	if ( arguments.length < 2 ) {
		clbk = arguments[ 0 ];
	} else {
		options = arguments[ 0 ];
		clbk = arguments[ 1 ];
		err = validate( opts, options );
		if ( err ) {
			throw err;
		}
	}
	if ( !isFunction( clbk ) ) {
		throw new TypeError( format( 'invalid argument. Callback argument must be a function. Value: `%s`.', clbk ) );
	}
	debug( 'Options: %s', JSON.stringify( opts ) );
	if ( opts.dir ) {
		dir = resolve( cwd(), opts.dir );
	} else {
		dir = cwd();
	}
	gopts = {
		'cwd': dir,
		'realpath': true // return absolute file paths
	};
	debug( 'Glob options: %s', JSON.stringify( gopts ) );

	debug( 'Searching for matching files...' );
	glob( opts.pattern, gopts, onGlob );

	/**
	* Callback invoked after matching files.
	*
	* @private
	* @param {(Error|null)} error - error object
	* @param {StringArray} names - list of matching files
	* @returns {void}
	*/
	function onGlob( error, names ) {
		var opts;
		if ( error ) {
			debug( 'Encountered an error when searching for matching files: %s', error.message );
			return clbk( error );
		}
		if ( names.length === 0 ) {
			debug( 'Found 0 matching files.' );
			return clbk( null, [] );
		}
		debug( 'Found %d matching files: %s', names.length, names.join( ',' ) );

		debug( 'Reading file contents...' );
		opts = {
			'encoding': 'utf8'
		};
		readFileList( names, opts, onRead );
	}

	/**
	* Callback invoked upon reading all file contents.
	*
	* @private
	* @param {(Error|null)} error - error object
	* @param {ObjectArray} files - file contents
	* @returns {void}
	*/
	function onRead( error, files ) {
		if ( error ) {
			debug( 'Encountered an error when reading file contents: %s', error.message );
			return clbk( error );
		}
		debug( 'Finished reading file contents.' );

		debug( 'Analyzing file ASTs...' );
		files = analyze( files );
		debug( 'Finished analysis.' );

		clbk( null, files );
	}
}
Asynchronously generates a list import and require paths.

@param {Options} [options] - function options
@param {string} [options.dir] - root directory from which to search for files
@param {string} [options.pattern='**\/*.js'] - file glob pattern
@param {Callback} clbk - callback to invoke upon completion
@throws {TypeError} callback argument must be a function
@throws {TypeError} options argument must be an object
@throws {TypeError} must provide valid options

@example
ls( onList );

function onList( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}