Binary search of a bounded interval of an integral type for the boundary of an upward-closed set, using a combination of exponential and binary search.
O(log(h-l)). Search a bounded interval of some integral type.
p is an upward-closed predicate,
searchFromTo p l h == Just n
if and only if
n is the least number
l <= n <= h satisfying
For example, the following function determines the first index (if any) at which a value occurs in an ordered array:
searchArray :: Ord a => a -> Array Int a -> Maybe Int searchArray x array = do let (lo, hi) = bounds array k <- searchFromTo (\ i -> array!i >= x) lo hi guard (array!k == x) return k