I have just written a function in Haskell that will perform a binary search on a list of integers. Pass it your list, the value you’re searching for, default low and high (0 and n-1) and it will return for you the position of your value. I’m sure there are plenty of experienced Haskell coders that will tell me there’s a better way, but I haven’t heard from one yet.

binsearch :: [Int] -> Int -> Int -> Int -> Int -- list, value, low, high, return int
binsearch xs value low high
   | high < low       = -1
   | xs!!mid > value  = binsearch xs value low (mid-1)
   | xs!!mid < value  = binsearch xs value (mid+1) high
   | otherwise        = mid
   where
   mid = low + ((high - low) `div` 2)