MCQs on Functions in Haskell | Haskell

Haskell Programming: Understanding Functions

Haskell is a functional programming language that relies heavily on functions for computation. To excel in Haskell, understanding how to define functions, use function application and currying, compose functions, and work with higher-order functions like map, filter, and fold is crucial. These concepts power Haskell’s expressive and efficient style.

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30 Multiple-Choice Questions on Functions in Haskell

Defining Functions

1. What is the syntax to define a function in Haskell?
   • A) functionName args = expression
   • B) def functionName(args):
   • C) function functionName(args)
   • D) let functionName = args => expression
2. Which keyword is used to define a local function within another function in Haskell?
   • A) let
   • B) where
   • C) do
   • D) in
3. How can you define a function with multiple cases in Haskell?
   • A) Using the if-else construct only
   • B) By writing multiple patterns with |
   • C) Using case or pattern matching
   • D) Using a switch statement
4. What happens if a function in Haskell does not cover all possible input patterns?
   • A) The function compiles but produces runtime errors for unhandled patterns.
   • B) The compiler fills the missing patterns automatically.
   • C) It will generate warnings but continue execution.
   • D) It will refuse to compile.
5. How do you declare a type signature for a function in Haskell?
   • A) functionName :: Type
   • B) def functionName : Type
   • C) let functionName = Type
   • D) type functionName = Type

Function Application and Currying

6. In Haskell, how is a function applied to its arguments?
   • A) By enclosing arguments in parentheses
   • B) By using whitespace between the function name and arguments
   • C) By using commas to separate arguments
   • D) By using a : separator
7. What is currying in Haskell?
   • A) A process of combining multiple functions into one
   • B) Transforming a function into a sequence of functions, each taking one argument
   • C) Making functions operate only on lists
   • D) Declaring multiple type signatures for a single function
8. What is the result of partially applying a function in Haskell?
   • A) A new function with fewer arguments
   • B) An error, since all arguments must be provided
   • C) The function is discarded
   • D) The partially applied function is automatically executed
9. What is the difference between f x y and f (x y) in Haskell?
   • A) f x y applies f to x and then to y, while f (x y) applies x to y first.
   • B) There is no difference; both are valid and equivalent.
   • C) f (x y) is invalid syntax.
   • D) f (x y) indicates that f is partially applied.
10. Which of the following is true about function application in Haskell?

• A) It is right-associative.
• B) It requires explicit parentheses for all arguments.
• C) It is left-associative.
• D) It requires type annotations every time.

Function Composition

11. What does the (.) operator do in Haskell?

• A) Multiplies two numbers
• B) Composes two functions such that (f . g) x = f (g x)
• C) Creates a tuple of two functions
• D) Concatenates two functions

12. How can you write the composition of f and g applied to x?

• A) f g x
• B) f (g x)
• C) (f x) . (g x)
• D) (f g) x

13. What is the primary benefit of using function composition in Haskell?

• A) It makes the code faster.
• B) It reduces the need for recursion.
• C) It creates cleaner and more readable code by avoiding intermediate variables.
• D) It allows functions to operate on lists directly.

14. How does function composition work with higher-order functions?

• A) Only one higher-order function can be composed at a time.
• B) Higher-order functions cannot be composed.
• C) Higher-order functions can be composed just like any other functions.
• D) Composition must involve intermediate variables for higher-order functions.

15. What is the type of the (.) operator in Haskell?

• A) (a -> b) -> (b -> c) -> (a -> c)
• B) (b -> a) -> (a -> c) -> (c -> b)
• C) (a -> b) -> (c -> a) -> (c -> b)
• D) (a -> b) -> (b -> a) -> (a -> b)

Higher-Order Functions

16. What is a higher-order function in Haskell?

• A) A function that only operates on numbers
• B) A function that takes another function as input or returns a function as output
• C) A function that cannot be partially applied
• D) A function that operates only on lists

17. Which of the following is an example of a higher-order function?

• A) map
• B) if-else
• C) let
• D) case

18. What does the map function do in Haskell?

• A) Transforms each element of a list using a given function
• B) Filters elements from a list based on a condition
• C) Reduces a list to a single value
• D) Creates a new list from the intersection of two lists

19. How does filter function work in Haskell?

• A) It applies a function to all elements of a list.
• B) It returns all elements of a list that satisfy a given predicate.
• C) It concatenates two lists.
• D) It creates a new list with unique elements only.

20. What is the purpose of foldl in Haskell?

• A) To transform a list into a single value by iterating from left to right
• B) To transform a list into a single value by iterating from right to left
• C) To concatenate two lists
• D) To map a function over a list

21. What is the key difference between foldl and foldr?

• A) foldl starts from the rightmost element, while foldr starts from the leftmost element.
• B) foldl processes the list left to right, while foldr processes it right to left.
• C) foldl works only on numbers, while foldr works on strings.
• D) There is no difference between the two.

22. How is map different from foldl?

• A) map creates a new list, while foldl reduces the list to a single value.
• B) map requires a predicate, while foldl does not.
• C) foldl works only with numbers, while map works with any type.
• D) foldl operates only on the last element of the list.

23. What is the type of the map function in Haskell?

• A) (a -> b) -> [a] -> b
• B) (a -> b) -> [a] -> [b]
• C) (a -> b) -> a -> [b]
• D) (a -> b) -> b -> [a]

24. How does the filter function handle an empty list?

• A) It throws an error.
• B) It returns Nothing.
• C) It returns an empty list.
• D) It concatenates two empty lists.

25. What does foldr (+) 0 [1, 2, 3] return in Haskell?

• A) 6
• B) 5
• C) 3
• D) 1

26. Which function can be used to check if all elements of a list satisfy a condition?

• A) map
• B) foldr
• C) all
• D) filter

27. Which higher-order function applies a function to elements of two lists simultaneously?

• A) map
• B) zipWith
• C) filter
• D) foldl

28. What does foldl (*) 1 [1, 2, 3] return?

• A) 6
• B) 5
• C) 1
• D) 0

29. How does foldl differ from scanl?

• A) foldl produces intermediate results, while scanl does not.
• B) scanl

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ChatGPT said:

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produces a list of accumulated results, while foldl only returns the final result.

• C) There is no difference; they are equivalent.
• D) scanl is used for numerical operations only.

30. What is the result of applying map (+1) to the list [1,2,3] in Haskell?

• A) [1, 2, 3]
• B) [2, 3, 4]
• C) [1, 3, 6]
• D) [3, 2, 1]

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Answers:

Qno	Answer (Option with the text)
1	A) functionName args = expression
2	A) let
3	B) By writing multiple patterns with `
4	A) The function compiles but produces runtime errors for unhandled patterns
5	A) functionName :: Type
6	B) By using whitespace between the function name and arguments
7	B) Transforming a function into a sequence of functions, each taking one argument
8	A) A new function with fewer arguments
9	A) f x y applies f to x and then to y, while f (x y) applies x to y first
10	A) It is right-associative.
11	B) Composes two functions such that (f . g) x = f (g x)
12	B) f (g x)
13	C) It creates cleaner and more readable code by avoiding intermediate variables
14	C) Higher-order functions can be composed just like any other functions
15	A) (a -> b) -> (b -> c) -> (a -> c)
16	B) A function that takes another function as input or returns a function as output
17	A) map
18	A) Transforms each element of a list using a given function
19	B) It returns all elements of a list that satisfy a given predicate
20	A) To transform a list into a single value by iterating from left to right
21	B) foldl processes the list left to right, while foldr processes it right to left
22	A) map creates a new list, while foldl reduces the list to a single value
23	B) (a -> b) -> [a] -> [b]
24	C) It returns an empty list
25	A) 6
26	C) all
27	B) zipWith
28	A) 6
29	B) scanl produces a list of accumulated results, while foldl only returns the final result
30	B) [2, 3, 4]