{-# LANGUAGE DeriveDataTypeable #-}

import Data.Data
import Data.Generics (listify)
import Data.List (nub, sortBy)
import Data.Maybe

data File = File String [Either File Module]
        deriving (Data, Typeable, Eq, Ord, Show)
data Module = Module String Component
        deriving (Data, Typeable, Eq, Ord, Show)
data Component = Component [File] [Module]
        deriving (Data, Typeable, Eq, Ord, Show)

f0 = File "f0" []
f1 = File "f1" []
f2 = File "f2" [Left f1]
f3 = File "f3" [Left f4, Left f5]
f4 = File "f4" []
f5 = File "f5" []
f6 = File "f6" [Right m3, Right m2]
f7 = File "f7" [Right m1, Left f0]
m1 = Module "m1" $ Component [f6] [m2, m3]
m2 = Module "m2" $ Component [f1, f2] []
m3 = Module "m3" $ Component [f3, f4, f5] []

testC = Component [f0, f7] [m1, m2, m3]

files :: [File]
files = nub $ listify (const True) testC

filesDeps :: [(String,[String])]
filesDeps = map (\(File n deps) -> (n, nub $ map fn $ listify (const True) deps)) files
        where
                fn (File n _) = n

compareDeps :: (String, [String]) -> (String, [String]) -> Ordering
compareDeps (fa, da) (fb, db)
        | fa `elem` db && fb `elem` da = error "cycle"
        | fa `elem` db = LT
        | otherwise = GT

sortedDeps = sortBy compareDeps filesDeps

*Main> mapM_ print sortedDeps
("f1",[])
("f2",["f1"])
("f5",[])
("f4",[])
("f3",["f4","f5"])
("f6",["f3","f4","f5","f1","f2"])
("f0",[])
("f7",["f6","f3","f4","f5","f1","f2","f0"])