Help with IF statement and sound

This code obviously isn’t right…I have a movie clip that either plays forwards or backwards with this actionscript at the start and at the end of the clip.
Can someone point me in the right direction?

Thanks in advance!

var msound = new Sound();
msound.attachSound(“mechwav”);
if (msound = true) {
msound.stop()
} else {
msound.start(0,1);
}