SICP exercises in Haskell (Section 2.1.4)

-- Section 2.1.4
-- Exercise 2.7
type Interval = (Float, Float)


make_interval :: Float -> Float -> Interval
make_interval x y = (x, y)


upper_bound :: Interval -> Float
upper_bound = snd


lower_bound :: Interval -> Float
lower_bound = fst


-- Exercise 2.8
sub_interval :: Interval -> Interval -> Interval
sub_interval x y =
  make_interval (lower_bound x - upper_bound y)
                (upper_bound x - lower_bound y)




-- To be continued. :)