如何從一個元組在Haskell

Question

提取元素，我有以下元組：

type Id = Int 
type Name = String 
type FSK = Int 
type Movie = (Id, Name, FSK) 

現在我想定義從一個給定的名單一樣，提取電影的功能：

extract :: Id -> [Movie] -> (Maybe Movie, [Movie]) 
extract = .... ?? 

這樣，當我給一個id和一個電影列表，它提取： 1）沒有+給定的列表，如果ID被發現 2）只是+電影，和沒有該電影的新列表，如果給定找到了id，並從列表中刪除了電影

例如：

*Main> extract 0 [(1,"Matrix",16),(2,"Gladiator",0)] 
(Nothing,[(1,"Matrix",16),(2,"Gladiator",0)]) 
*Main> extract 1 [(1,"Matrix",16),(2,"Gladiator",0)] 
(Just (1,"Matrix",16),[(2,"Gladiator",0)]) 

我應該如何定義函數？

Answer 1

extract :: Id -> [Movie] -> (Maybe Movie, [Movie]) 
extract id []     = (Nothing, []) 
extract id ((fid, n, f):list) | fid == id = (Just (fid, n, f), list) 
           | otherwise = (found, (fid, n, f):tail) 
           where (found, tail) = extract id list