This solution fails for ambiguous sampling.

signal = "11111111000000"
discrete = map length . group $ signal

minimum discrete == 6
foldl' gcd 0 discrete == 2

There's an option to switch to TypeScript ES6, which supports String.prototype.repeat.

I had the same problem, but it just means there's something else wrong with your code.

Sometimes the errors you get back don't make any sense.

prop_ext_eq n k = n >= 1 && n <= 10000 && k >= 1 && k <= 100 ==> twoByN n k == twoByN' n k
It generates integers by

instance Arbitrary Integer where
  arbitrary = arbitrarySizedIntegral
  shrink    = shrinkIntegral

where

arbitrarySizedIntegral =
  sized $ \n ->
  inBounds fromInteger (choose (-toInteger n, toInteger n))

first, then checks the constraint, so the upper bound of n is about 100 here.

prop_ext_eq n k = n >= 1 && n <= 10000 && k >= 1 && k <= 100 ==> twoByN n k == twoByN' n k
It generates integers by

instance Arbitrary Integer where
  arbitrary = arbitrarySizedIntegral
  shrink    = shrinkIntegral

where

arbitrarySizedIntegral =
  sized $ \n ->
  inBounds fromInteger (choose (-toInteger n, toInteger n))

first, then checks the constraint, so the upper bound of n is about 100 here.