faust-一个简单的单选下拉菜单代码，用于切换波形。

import("stdfaust.lib");
waveSelector = vslider("WaveShapes[style:menu{'Sin':0;'Tri':1,'Saw':2,'Square':3}]",0,0,4,1);
freq = hslider("Freq",20,20,2000,1);
wave = (os.osc(freq),os.triangle(freq),os.sawtooth(freq),os.square(freq)): ba.selectn(4,waveSelector);
process = wave;