こういうこと？
screen 0,320,320 : x = 160 : y = 160
dx = 0,-1,0,0,1,0,0,0,0
dy = 0,0,-1,0,0,0,0,0,1
repeat
redraw 0
pos x,y : color 255,255,255 : print "●"
stick a
if a!0 : b = a&15
x = (x+dx.b+winx)\winx : y = (y+dy.b+winy)\winy
pos x,y : color 0,0,0 : print "●"
redraw 1
await 10
loop