Missed Mid-Term Solutions

Assets/Solutions/Mid-Term/Missed-Mid-Term.md

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+# 20CYS312 - Principles of Programming Languages
+![](https://img.shields.io/badge/Batch-21CYS-lightgreen) ![](https://img.shields.io/badge/UG-blue) ![](https://img.shields.io/badge/Subject-PPL-blue) <br/>
+![](https://img.shields.io/badge/Lecture-2-orange) ![](https://img.shields.io/badge/Practical-3-orange) ![](https://img.shields.io/badge/Credits-3-orange)
+
+## Missed Mid-Term Question Paper with Solutions
+
+#### 1. Write the \textit{type signature} of the below functions.
+(a) drop   <br/>
+(b) map   <br/>
+(c) concat   <br/>
+
+#### 2. Write a function _pairwiseConcat_ in Haskell that takes two lists of strings and concatenates them pairwise. 
+If one list is longer than the other, the extra elements should be ignored.
+Usage Example:
+ 1.  \> _pairwiseConcat_ [”a”, ”b”, ”c”] [”x”, ”y”, ”z”]
+       [”ax”, ”by”, ”cz”]
+ 2.  \> _pairwiseConcat_ [”hello”, ”world”] [”!”, ”?”, ”!!”]
+       ["hello!", "world?"]
+ 3.  \> pairwiseConcat [] [”a”, ”b”, ”c”]
+       []
+
+**Solution:**
+```
+
+```
+
+#### 4. Write the equivalent to the following map and filter expression using list comprehension
+(a) map reverse (filter (even . length) strs) <br/>
+(b) map length (filter (\word → length word > 10) words)  <br/>
+
+
+**Solution:** <br/>
+(a) **[ reverse s | s ← strs, even (length s) ]** <br/>
+(b) **[ length word | word ← words, length word > 5 ]** <br/>
+
+
+#### 6. Complete the Haskell implementation of BinaryTree and trace the output step by step. ????? should be filled to complete the program
+
+**Solution:**
+```
+-- Define a binary tree data type
+data BinaryTree a = EmptyTree | Node a (BinaryTree a) (BinaryTree a) deriving (?????)
+
+-- Function to insert an element into a binary tree
+insert :: (Ord a) => a -> BinaryTree a -> BinaryTree a
+insert x ????? = Node x EmptyTree EmptyTree
+insert x (Node a left right)
+| x == a = Node x left right
+| x ????? a = Node a (insert x left) right
+| x ????? a = Node a left (insert x right)
+
+-- Function to check if an element is present in the binary tree
+search :: (Ord a) => a -> BinaryTree a -> ?????
+search _ EmptyTree = False
+search x (Node a left right)
+| x == a = True
+| x < a = search x left
+| x > a = search x right
+
+-- Usage
+examTree :: BinaryTree Int
+examTree = ????? insert EmptyTree [78, 14, 03, 89]
+
+main :: IO ()
+main = do
+print examTree
+putStrLn $ "Is 89 in the tree? " ++ show (search 89 examTree)
+putStrLn $ "Is 90 in the tree? " ++ show (search 90 examTree)
+```
+
+#### 7. Identify the key characteristic of Haskell that underscores its focus on composing functions and data structures to create concise and expressive code
+**Solution:** Higher-order functions
+
+
+#### 8. Complete the following Haskell function _sumPositive_.
+```
+-- Consider the following incomplete Haskell function definition for summing
+all positive elements in a list
+sumPositive :: [Int] -> Int
+sumPositive [] = ???
+sumPositive (x:xs) = ???
+-- Your task is to complete the definition of the ’sumPositive’ function to
+correctly calculate the sum of all positive elements in the given list ’xs’.
+-- Assumption: the list ’xs’ is not empty.
+```
+**Solution:**
+```
+
+```
+
+#### 9. Given the following _data_ type declaration, What does the function getValue return when provided with 6 as input?
+```
+data Result = Success Int | Failure
+
+processValue :: Int -> Result
+processValue x =
+    if x > 0
+    then Success (x * 2)
+    else Failure
+
+getValue :: Int -> Maybe Result
+getValue x =
+    if x `mod` 2 == 0
+    then Just (processValue x)
+    else Nothing
+```
+**Solution:** Just (Success 12)