在上 FLOLAC 的課程時，老師出了一些 Haskell 的練習題給我們練習。
這邊我列出第三部分的題目跟我作的參考答案~ (練習使用 List 跟寫遞回函數!)
但我還是建議你看原版的PDF (有全部的題目) 會比較清楚XD
When I am studying in the FLOLAC, the teacher gave us some Haskell exercises to practice.
I put the problems and my answer of section 3 to this article! ( for List and recursive functions.)
But I think you should see the original practicals PDF, which is more clear.
1. Define a function fstEven :: [Int] → Int that returns the first even number of the input list.
2. Define a function hasZero :: [Int] → Bool that returns True if and only if there is a 0 in the input list.
3. Define a function myLast that takes a list and returns the last (rightmost) element.
(a) Let the type be myLast :: [a] → a. Define myLast.
(b) What happens in the previous definition of the input list is empty?
(c) Define myLast :: [a] → Maybe a, which returns Nothing if the list is empty.
4. Define a function pos such that pos x xs looks for x in xs and returns its position.
For example, find 'a' "abc" yields 0, and find 'a' "bac" yields 1.
(a) Let the type be pos :: Eq a ⇒ a → [a] → Int. In your definition, what happens if x is not in the list?
(b) Let the type be pos :: Eq a ⇒ a → [a] → Maybe Int, such that pos x xs returns Nothing if x is not in the list.
5. Define myConcat :: [[a]] → [a] such that, for example myConcat [[1,2,3], [], [4], [5,6]] = [1,2,3,4,5,6]. Hint: use (++).
6. Define double :: [a] → [a] such that, for example, double [1,2,3] = [1,1,2,2,3,3].
7. Define interleave :: [a] → [a] → [a] such that, for example, interleave [1,2,3,4] [5,6,7] = [1,5,2,6,3,7,4].
8. Define splitLR :: [Either a b] → ([a], [b]) such that, for example:
splitLR [Left 1, Left 3, Right 'a', Left 2, Right 'b'] = ([1,3,2], "ab") .
9. Define a function fan :: a → [a] → [[a]] such that fan x xs inserts x into the 0th, 1st. . . nth positions of xs, where n is the length of xs. For example:
fan 5 [1,2,3,4] = [[5,1,2,3,4], [1,5,2,3,4], [1,2,5,3,4], [1,2,3,5,4], [1,2,3,4,5]] .
10. Define perms :: [a] → [[a]] that returns all permutations of the input list. For example:
perms [1,2,3] = [[1,2,3], [2,1,3], [2,3,1], [1,3,2], [3,1,2], [3,2,1]] .
11. Try to define functions inits and tails yourself, and make sure you understand them. Recall that inits [1,2,3] = [[ ], [1], [1,2], [1,2,3]], and tails [1,2,3] = [[1,2,3], [2,3], [3], [ ]].
我作的參考解答(有給老師改過了XD，應該沒有問題~)
Here is my answer. (The teacher has saw that so I think it's correct.)
這邊我列出第三部分的題目跟我作的參考答案~ (練習使用 List 跟寫遞回函數!)
但我還是建議你看原版的PDF (有全部的題目) 會比較清楚XD
When I am studying in the FLOLAC, the teacher gave us some Haskell exercises to practice.
I put the problems and my answer of section 3 to this article! ( for List and recursive functions.)
But I think you should see the original practicals PDF, which is more clear.
練習題目 Practicals: 3 Inductively Defined Functions on Lists
1. Define a function fstEven :: [Int] → Int that returns the first even number of the input list.
2. Define a function hasZero :: [Int] → Bool that returns True if and only if there is a 0 in the input list.
3. Define a function myLast that takes a list and returns the last (rightmost) element.
(a) Let the type be myLast :: [a] → a. Define myLast.
(b) What happens in the previous definition of the input list is empty?
(c) Define myLast :: [a] → Maybe a, which returns Nothing if the list is empty.
4. Define a function pos such that pos x xs looks for x in xs and returns its position.
For example, find 'a' "abc" yields 0, and find 'a' "bac" yields 1.
(a) Let the type be pos :: Eq a ⇒ a → [a] → Int. In your definition, what happens if x is not in the list?
(b) Let the type be pos :: Eq a ⇒ a → [a] → Maybe Int, such that pos x xs returns Nothing if x is not in the list.
5. Define myConcat :: [[a]] → [a] such that, for example myConcat [[1,2,3], [], [4], [5,6]] = [1,2,3,4,5,6]. Hint: use (++).
6. Define double :: [a] → [a] such that, for example, double [1,2,3] = [1,1,2,2,3,3].
7. Define interleave :: [a] → [a] → [a] such that, for example, interleave [1,2,3,4] [5,6,7] = [1,5,2,6,3,7,4].
8. Define splitLR :: [Either a b] → ([a], [b]) such that, for example:
splitLR [Left 1, Left 3, Right 'a', Left 2, Right 'b'] = ([1,3,2], "ab") .
9. Define a function fan :: a → [a] → [[a]] such that fan x xs inserts x into the 0th, 1st. . . nth positions of xs, where n is the length of xs. For example:
fan 5 [1,2,3,4] = [[5,1,2,3,4], [1,5,2,3,4], [1,2,5,3,4], [1,2,3,5,4], [1,2,3,4,5]] .
10. Define perms :: [a] → [[a]] that returns all permutations of the input list. For example:
perms [1,2,3] = [[1,2,3], [2,1,3], [2,3,1], [1,3,2], [3,1,2], [3,2,1]] .
11. Try to define functions inits and tails yourself, and make sure you understand them. Recall that inits [1,2,3] = [[ ], [1], [1,2], [1,2,3]], and tails [1,2,3] = [[1,2,3], [2,3], [3], [ ]].
我作的參考解答(有給老師改過了XD，應該沒有問題~)
Here is my answer. (The teacher has saw that so I think it's correct.)
推薦相關文章給您:
1. 安裝Haskell環境與基本操作教學 - 使用GHCi
2. Haskell Practicals 1 - Functions 函數
3. Haskell Practicals 2 - Products and Sums 乘積和合
4. Haskell Practicals 3 - Lists and Recursive Function 遞回函數
If you want to use (copy, paste or quote) my original article, please contact me through email. (autek.roy@gmail.com) If there is any mistake or comment, please let me know. :D
如要使用(複製貼上或轉載)作者原創文章， 請來信跟我聯絡。(autek.roy@gmail.com) 如果有發現任何的錯誤與建議請留言或跟我連絡。 : )
沒有留言:
張貼留言
請留下您的任何想法或建議!
Please leave any thought or comment!