the hackvm documentation says:
'v' Remove S<S0+1> from the stack and push it on top (ex: 0v swaps S0 and S1)
i think it's meant to say '1v swaps s0 and s1'
because code:
010v
stack is
0 [0]
1 [0,1]
0 [0,1,0]
v [0,1]
0,1 are not getting switched.