A “Demo”

prop_Insert :: Integer -> [Integer] -> Property

prop_Insert x xs =

ordered xs ==>

collect (length xs) $ ordered (insert x xs)

ordered xs = and (zipWith (<=) xs (drop 1 xs))

Main> quickCheck prop_Insert

OK, passed 100 tests.

46% 0.

26% 1.

19% 2.

8% 3.

1% 4.

A random list is

unlikely to be ordered

unless it is very short!