`oneOf` and `elements` never yield the last element

[David Peter]

Currently, oneOf is implemented as

oneOf :: forall a. Gen a -> Array (Gen a) -> Gen a
oneOf x xs = do
  n <- chooseInt zero (length xs)
  if n < one then x else fromMaybe x (xs !! (n - one))

Apparently, chooseInt a b returns a random integer from the set a, a + 1, ..., b - 1, excluding the value b. Consequently, the maximum value for the index n - one in the last line is length xs - 2 and the last element of xs will never be chosen:

> showSample (oneOf (pure 1) [pure 2])
[1,1,1,1,1,1,1,1,1,1]

The same is true for elements.

[Phil Freeman]

👍 Thanks!