Numeric.Search.Range

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.

Documentation

searchFromTo :: Integral a => (a -> Bool) -> a -> a -> Maybe a

O(log(h-l)). Search a bounded interval of some integral type.

If 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 p.

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