The One And Only Negative Machine! :D (there may be others though. D:)

reset
cleartext
to Negative_Machine :Negative :n
if :Negative = 0[
  output :n
]
if :Negative = 1[
  output :n - 2 * :n
]
end
print Negative_Machine 0 100
print Negative_Machine 1 1.75