SICP's amb is the list monad, by example

Amb.hs

-- You can find the original in section 4.3.2 of SICP: http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-28.html#%_sec_4.3.2

import Data.List

distinct :: Eq a => [a] -> Bool
distinct xs = length (nub xs) == length xs

require :: Bool -> [[a]] -> [[a]]
require b e = if b then e else return []

data Name = Baker | Cooper | Fletcher | Miller | Smith
    deriving (Show, Eq)

multipleDwelling :: [[(Name, Int)]]
multipleDwelling = filter (not . null) $ do
    baker <- [1, 2, 3, 4, 5]
    cooper <- [1, 2, 3, 4, 5]
    fletcher <- [1, 2, 3, 4, 5]
    miller <- [1, 2, 3, 4, 5]
    smith <- [1, 2, 3, 4, 5]
    
    require (distinct [baker, cooper, fletcher, miller, smith]) $
        require (not (baker == 5)) $
            require (not (cooper == 1)) $
                require (not (fletcher == 5)) $
                    require (not (fletcher == 1)) $
                        require (miller > cooper) $
                            require (not (abs (smith - fletcher) == 1)) $
                                require (not (abs (fletcher - cooper) == 1)) $
                                    return [ (Baker, baker)
                                           , (Cooper, cooper)
                                           , (Fletcher, fletcher)
                                           , (Miller, miller)
                                           , (Smith, smith)
                                           ]

-- And indeed, when we run this, we get:
--     *Main> multipleDwelling 
--     [[(Baker,3),(Cooper,2),(Fletcher,4),(Miller,5),(Smith,1)]]