use Nat drop

use Optional None Some

search : (Nat -> Int) -> Nat -> Nat -> Optional Nat

search hit bot top =

go : Nat -> Nat -> Optional Nat

go bot top =

if bot >= top then None

else

mid = (bot + top) / 2

match hit mid with

+0 -> Some mid

-1 -> go bot (drop mid 1)

+1 -> go (mid + 1) top

go bot top