function f()
  sys a=1,b=2,c=3,d=4
  push a
  push b
  push c
  push d
  print a "," b "," c "," d 'result 1,2,3,4
  a=10
  b=20
  c=30
  d=40
  print a "," b "," c "," d 'result 10,20,30,40
  pop a
  pop b
  pop c
  pop d
  print a "," b "," c "," d 'result 4,3,2,1
end function

f