You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
63 lines
1.5 KiB
63 lines
1.5 KiB
7 years ago
|
module Rewrite where
|
||
|
|
|
||
|
|
-- 1
|
||
|
|
myOr :: [Bool] -> Bool
|
||
|
|
myOr = foldr (||) False
|
||
|
|
|
||
|
|
-- 2
|
||
|
|
myAny :: (a -> Bool) -> [a] -> Bool
|
||
|
|
myAny f = foldr (\a b -> f a || b) False
|
||
|
|
|
||
|
|
-- 3
|
||
|
|
myElem :: Eq a => a -> [a] -> Bool
|
||
|
|
myElem x = foldr (\a b -> (x == a) || b) False
|
||
|
|
|
||
|
|
myElem' :: Eq a => a -> [a] -> Bool
|
||
|
|
myElem' x = any (x==)
|
||
|
|
|
||
|
|
-- 4
|
||
|
|
myReverse :: [a] -> [a]
|
||
|
|
myReverse = foldr (\a b -> b ++ [a]) []
|
||
|
|
-- other solution would be to use foldl (flip (:)) []
|
||
|
|
|
||
|
|
-- 5
|
||
|
|
myMap :: (a -> b) -> [a] -> [b]
|
||
|
|
myMap f = foldr (\a b -> f a : b) []
|
||
|
|
-- myMap = foldr ((:) . f) []
|
||
|
|
|
||
|
|
-- 6
|
||
|
|
myFilter :: (a -> Bool) -> [a] -> [a]
|
||
|
|
myFilter f = foldr g []
|
||
|
|
where g a b
|
||
|
|
| f a = a : b
|
||
|
|
| otherwise = b
|
||
|
|
|
||
|
|
-- 7
|
||
|
|
squish :: [[a]] -> [a]
|
||
|
|
squish = foldr (++) []
|
||
|
|
|
||
|
|
-- 8
|
||
|
|
squishMap :: (a -> [b]) -> [a] -> [b]
|
||
|
|
squishMap f = foldr ((++) . f) []
|
||
|
|
|
||
|
|
-- 9
|
||
|
|
squishAgain :: [[a]] -> [a]
|
||
|
|
squishAgain = squishMap id
|
||
|
|
|
||
|
|
-- 10
|
||
|
|
myMaximumBy :: (a -> a -> Ordering) -> [a] -> a
|
||
|
|
myMaximumBy _ [] = undefined
|
||
|
|
myMaximumBy _ [x] = x
|
||
|
|
myMaximumBy f (x:xs) = foldl go x xs
|
||
|
|
where go a b
|
||
|
|
| f a b == GT = a
|
||
|
|
| otherwise = b
|
||
|
|
|
||
|
|
-- 11
|
||
|
|
myMinimumBy :: (a -> a -> Ordering) -> [a] -> a
|
||
|
|
myMinimumBy _ [] = undefined
|
||
|
|
myMinimumBy _ [x] = x
|
||
|
|
myMinimumBy f (x:xs) = foldl go x xs
|
||
|
|
where go a b
|
||
|
|
| f a b == LT = a
|
||
|
|
| otherwise = b
|