label 1

# read a char and put copies on the stack
push 0
readchar
push 0
retrieve

# compate to EOF and jump to end if it matches
dup
push -1
sub
jz 5

# compare to \t and jump to 3 if it matches 
dup
push 9
sub
jz 3
jump 2

# non-tab
label 2
outchar
jump 4

# tab
label 3
discard
push 32
dup
dup
dup
outchar
outchar
outchar
outchar
jump 4

# goto start
label 4
jump 1

# end
label 5
exit