A little working example of Haskell's 'comprehensive comprehensions' as supported by the TransformListComp extension.

gistfile1.hs

{-# LANGUAGE TransformListComp #-}

-- There are three new keywords: group, by, and using. 
-- The functions sortWith and groupWith are not keywords; they are ordinary functions that are exported by GHC.Exts.)
import GHC.Exts (sortWith, groupWith)

--import Data.List (sort)

-- actual syntax: http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#generalised-list-comprehensions
--
-- original paper: http://research.microsoft.com/en-us/um/people/simonpj/papers/list-comp/list-comp.pdf
--
-- this extension can also do CUBE aggregation instead of just relational stuff!

type Name = String
type Dept = String
type Salary = Int


employees :: [(Name,     Dept,   Salary)]
employees = [ ("Simon",  "MS",   80)
            , ("Erik",   "MS",   100)
            , ("Phil",   "Ed",   40)
            , ("Gordon", "Ed",   45)
            , ("Paul",   "Yale", 60)]

foo3 = [ (dept, sum salary)
       | (name, dept, salary) <- employees
       , then group by dept using groupWith
       , then sortWith by (sum salary)
       , then take 5 ]

foo1 = 
  map (\(name, salary) -> name)
    (sortWith (\(name, salary) -> salary)
      [ (name, salary)
      | (name, dept, salary) <- employees
      , salary < 50 ])



main = do
--  putStrLn $ show foo1
--  putStrLn $ show foo2
  putStrLn $ show foo3
--  putStrLn $ map show foo


-- this library function removes duplicates in a list
-- nub :: Eq a => [a] -> [a]