从haskell的列表中找到最小偶数

Question

Please help me write a function in haskell which would help me find a minimum even number in a list. Incase the list contains all the odd number throw an exception. I am able to write two separate functions but not able to write one complete program. My code is as follows.

retainEven :: [Int] -> [Int]
retainEven [] = []
retainEven (n:ns)= 

    if ((mod n 2) == 0)
        then n : (retainEven ns) 
    else retainEven ns


enter code here




mymin [] = error "no element" 
mymin [x] = x  
mymin (x:y:xs) = mymin ((if x < y then x else y):xs)

Answer 1

过滤偶数元素，然后取最小值：

minEvens = minimum . filter even