binarySearch .hs

binSearch :: Integral i => (i -> Bool) -> i -> i -> i
binSearch f = go where
    go l h
        | l > h     = l
        | f m       = go l (m - 1)
        | otherwise = go (m + 1) h
        where m = (l + h) `div` 2

binSearchA :: (a -> Bool) -> Array Int a -> Int
binSearchA f a = binSearch (f . (a!)) l h where (l, h) = bounds a