fn compose<P,R0,R1,F0,F1,FR>(mut f0:F0,mut f1:F1)->FR
where
    F0:FnMut(P)->R0,
    F1:FnMut(R0)->R1,
    FR:FnMut(P)->R1,
{
    move|x|{
        let x=f0(x);
        f1(x)
    }
}
fn main(){
    let mut func=compose(|x|x+2,|x|x*2);
    assert_eq!(4,func(0));
    assert_eq!(6,func(1));
    assert_eq!(8,func(2));
}