list.hs

type MemberId = Int
type ItemId = Int

data Sex = Man | Woman deriving (Show,Eq)

data Member = Member {
  memberId :: MemberId
  ,memberName :: String
  ,memberSex :: Sex
  } deriving (Show)
              
type MemberDB = [Member]

membersBySex :: MemberDB -> Sex -> [Member]
membersBySex db sex = filter (\m -> memberSex m == sex) db


data Item = Item {
  itemId :: ItemId
  ,itemName :: String
  } deriving (Show)

type MemberItemDB = [(MemberId,Item)]


itemsByMember :: MemberItemDB -> MemberId -> [Item]
itemsByMember db memberId =
  let items = filter (\(id,_) -> id == memberId) db
  in map snd items



itemsBySex :: MemberDB -> MemberItemDB -> Sex -> [String]
itemsBySex mdb idb sex =
  concat $ map (\member->
                 map (\item ->
                       (memberName member) ++ ":" ++ (itemName item)
                     ) $ itemsByMember idb $ memberId member
               ) $ membersBySex mdb sex
  
  
itemsBySexM :: MemberDB -> MemberItemDB -> Sex -> [String]
itemsBySexM mdb idb sex = do
  member <- membersBySex mdb sex
  item <- itemsByMember idb $ memberId member
  return $ (memberName member) ++ ":" ++ (itemName item)




main = do
  print $ itemsBySex
    [
      Member 101 "1st" Man,
      Member 102 "2nd" Woman,
      Member 103 "3rd" Man,
      Member 104 "4th" Woman
    ]
    [
      (101, Item 1001 "item1001"),
      (101, Item 1002 "item1002"),
      (101, Item 1003 "item1003"),
      (102, Item 1004 "item1004"),
      (102, Item 1005 "item1005"),
      (102, Item 1006 "item1006"),
      (103, Item 1007 "item1007"),
      (103, Item 1008 "item1008"),
      (103, Item 1009 "item1009"),
      (104, Item 1010 "item1010"),
      (104, Item 1011 "item1011"),
      (104, Item 1012 "item1012")
    ]
    Man

  print $ itemsBySexM
    [
      Member 101 "1st" Man,
      Member 102 "2nd" Woman,
      Member 103 "3rd" Man,
      Member 104 "4th" Woman
    ]
    [
      (101, Item 1001 "item1001"),
      (101, Item 1002 "item1002"),
      (101, Item 1003 "item1003"),
      (102, Item 1004 "item1004"),
      (102, Item 1005 "item1005"),
      (102, Item 1006 "item1006"),
      (103, Item 1007 "item1007"),
      (103, Item 1008 "item1008"),
      (103, Item 1009 "item1009"),
      (104, Item 1010 "item1010"),
      (104, Item 1011 "item1011"),
      (104, Item 1012 "item1012")
    ]
    Man

--  print $ membersBySex [
--    Member 101 "1st" Man,
--    Member 102 "2nd" Woman,
--    Member 103 "3rd" Man,
--    Member 104 "4th" Woman
--    ] Man
--
--  print $ itemsByMember [
--    (101, Item 1001 "item1001"),
--    (101, Item 1002 "item1002"),
--    (101, Item 1003 "item1003"),
--    (102, Item 1004 "item1004"),
--    (102, Item 1005 "item1005"),
--    (102, Item 1006 "item1006"),
--    (103, Item 1007 "item1007"),
--    (103, Item 1008 "item1008"),
--    (103, Item 1009 "item1009"),
--    (104, Item 1010 "item1010"),
--    (104, Item 1011 "item1011"),
--    (104, Item 1012 "item1012")
--    ] 101