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@mitsuji
Last active January 10, 2016 01:43
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import Data.Maybe (isNothing,fromJust)
type ID = Int
type Rank = Int
type Name = String
type RankDB = [(Rank,ID)]
type NameDB = [(ID,Name)]
idFromRank :: RankDB -> Rank -> Maybe ID
idFromRank db rk = lookup rk db
nameFromId :: NameDB -> ID -> Maybe Name
nameFromId db id = lookup id db
topThree :: RankDB -> NameDB -> Maybe (Name,Name,Name)
topThree rdb ndb =
let maybeId1 = idFromRank rdb 1
in
if isNothing maybeId1 then Nothing
else
let maybeName1 = nameFromId ndb $ fromJust maybeId1
in
if isNothing maybeName1 then Nothing
else
let maybeId2 = idFromRank rdb 2
in
if isNothing maybeId2 then Nothing
else
let maybeName2 = nameFromId ndb $ fromJust maybeId2
in
if isNothing maybeName2 then Nothing
else
let maybeId3 = idFromRank rdb 3
in
if isNothing maybeId3 then Nothing
else
let maybeName3 = nameFromId ndb $ fromJust maybeId3
in
if isNothing maybeName3 then Nothing
else Just (
fromJust maybeName1,
fromJust maybeName2,
fromJust maybeName3
)
topThreeC :: RankDB -> NameDB -> Maybe (Name,Name,Name)
topThreeC rdb ndb =
case idFromRank rdb 1 of
Nothing -> Nothing
Just id1 -> case nameFromId ndb id1 of
Nothing -> Nothing
Just n1 -> case idFromRank rdb 2 of
Nothing -> Nothing
Just id2 -> case nameFromId ndb id2 of
Nothing -> Nothing
Just n2 -> case idFromRank rdb 3 of
Nothing -> Nothing
Just id3 -> case nameFromId ndb id3 of
Nothing -> Nothing
Just n3 -> Just (n1,n2,n3)
topThreeM :: RankDB -> NameDB -> Maybe (Name,Name,Name)
topThreeM rdb ndb = do
id <- idFromRank rdb 1
n1 <- nameFromId ndb id
id <- idFromRank rdb 2
n2 <- nameFromId ndb id
id <- idFromRank rdb 3
n3 <- nameFromId ndb id
return (n1,n2,n3)
main = do
print $ topThree [(1,101),(2,102),(3,103)] [(101,"1st"),(102,"2nd"),(103,"3rd")]
print $ topThree [(1,101),(4,102),(3,103)] [(101,"1st"),(102,"2nd"),(103,"3rd")]
print $ topThree [(1,101),(2,102),(3,103)] [(101,"1st"),(104,"4th"),(103,"3rd")]
print $ topThreeC [(1,101),(2,102),(3,103)] [(101,"1st"),(102,"2nd"),(103,"3rd")]
print $ topThreeC [(1,101),(4,102),(3,103)] [(101,"1st"),(102,"2nd"),(103,"3rd")]
print $ topThreeC [(1,101),(2,102),(3,103)] [(101,"1st"),(104,"4th"),(103,"3rd")]
print $ topThreeM [(1,101),(2,102),(3,103)] [(101,"1st"),(102,"2nd"),(103,"3rd")]
print $ topThreeM [(1,101),(4,102),(3,103)] [(101,"1st"),(102,"2nd"),(103,"3rd")]
print $ topThreeM [(1,101),(2,102),(3,103)] [(101,"1st"),(104,"4th"),(103,"3rd")]
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