Im trying to make it so you pres left and righ to turn and up and down to go forward and back. All i can do with this coding is turn:

mob
Move(var/m, var/n) if(src.density)
if(n == NORTH)
step(usr,usr.dir)
else if(n == EAST)
usr.dir = turn(usr.dir, -45)
else if(n == WEST)
usr.dir = turn(usr.dir, 45)
else if(n == SOUTH)
step(usr, turn(usr.dir, 180))
usr.dir = turn(usr.dir, 180)

Why cant i go forward and back? THanks!