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