如何从一个元组在Haskell

Question

提取元素，我有以下元组：

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

现在我想定义从一个给定的名单一样，提取电影的功能：

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

这样，当我给一个id和一个电影列表，它提取： 1）没有+给定的列表，如果ID被发现 2）只是+电影，和没有该电影的新列表，如果给定找到了id，并从列表中删除了电影

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)]) 

我应该如何定义函数？

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