gistfile1.hs

:set +m

import qualified Data.Map


let phoneBook = [("betty","555-2938")
                ,("betty","342-2492")
                ,("bonnie","452-2928")
                ,("patsy","493-2928")
                ,("patsy","943-2929")
                ,("patsy","827-9162")
                ,("lucille","205-2928")
                ,("wendy","939-8282")
                ,("penny","853-2492")
                ,("penny","555-2111")
                ]

let phoneBookMap = Data.Map.fromList [("betty",["555-2938","342-2492"])
                                     ,("bonnie",["452-2928"])
                                     ,("lucille",["205-2928"])
                                     ,("patsy",["493-2928","943-2929","827-9162"])
                                     ,("penny",["853-2492","555-2111"])
                                     ,("wendy",["939-8282"])
                                     ]



Data.Map.fromListWith (flip (++)) [(a,[b]) | (a,b) <- phoneBook] == phoneBookMap
-- True