Yr1 Functional Programming

Question 1

What is a pure function?

Answer 1

Consistent functions that always output the same result for the same input.
They don’t alter external variables or code.

Question 2

What is ideal when programming with functions?

Answer 2

Only use pure functions.
i.e. functions shouldn’t alter external variables or code.

Question 3

What is ideal when programming with functions?

Answer 3

Only use pure functions.
i.e. functions shouldn’t alter external variables or code.

Question 4

Wha is immutability?

Answer 4

Once a variable is created it shouldn’t be altered. Meaning any functions applied to it should create a new variable for the result.

Question 5

What 2 ideas are essential for proper functional programming?

Answer 5

1. Only use pure functions
2. Variables should be immutable

Question 6

What are the 4 benefits of functional programming?

Answer 6

1. Code is easier to test as function can be tested individually
2. Code has fewer bugs due to lack of side effects from functions
3. Code is easier to understand
4. Coding is faster

Question 7

What is Haskell?

Answer 7

A specific functional programming language.

Question 8

Write down the Haskell code for creating a function that doubles a variable x:

Answer 8

let double x = x+x
To call:
double 5
Output:
10

Question 9

Create a Haskell function for x-y

Answer 9

let minus xy = x-y
To call:
minus 10 5
Output:
5

Question 10

What is a domain?

Answer 10

The input of a function

Question 11

What is the Co Domain?

Answer 11

The output of a function

Question 12

How are the domain and co domain of a function displayed in Haskell? Give an example

Answer 12

IsEven :: Int -> Bool
Domain is an integer and Co Domain is a Boolean.

Question 13

What is a composite function?

Answer 13

A function represented using a dot between two other functions.
The same as doing f(g(x)) but looks like: f.g (use a circle instead of the dot usually

Question 14

What is a higher order function?

Answer 14

HOFs are functions that can take and return given functions as parameters/results

Question 15

What are the 3 main higher order functions?

Answer 15

1. Map
2. Filter
3. Reduce/fold

Question 16

What does the higher order function map do?

Answer 16

Applies the given function to a given list. Notation:
let numbers=[1,2,3,4]
map (double) numbers

The code above doubles all the numbers in the list (double would have to be defined) and returns the list of doubled numbers

Question 17

What does the higher order function filter do?

Answer 17

Takes a condition and a list and returns a list containing all numbers that met the condition.
E.g.
let numbers = [1,2,3,4]
filter (<16) numbers

Question 18

What does the higher order function fold do?

Answer 18

Combines all the numbers in a list into one. The type of combination can be specified e.g. * or - or +
foldl (+) 0 numbers
Function above adds all the number in a list and returns the result. Starts with 0.
foldl starts from left and foldr starts from right.

Question 19

What does && do in Haskell?

Answer 19

And gate

Question 20

What does || do in Haskell?

Answer 20

Or gate

Question 21

Write the Haskell notation for inverting the Boolean value x

Answer 21

not(x)

Question 22

Wirte the notation for the 5 useful functions in Haskell?

Answer 22

1. head myList, returns head of the list
2. tail myList, returns tail of the list
3. null myList, checks if the list is empty
4. length myList, returns length of list
5. 15:myList, prepends 15 to the list
6. myList++15, appends 15 to the list

Question 23

What is recursion?

Answer 23

When a function calls itself to solve a problem step by step.

Question 24

What is the exit clause for a recursive function called?

Answer 24

The base case

Question 25

How is a base case defined in Haskell?

Answer 25

factorial 0 =1 Above code defines the base case for below function: factorial x =x*factorial(x-1)

Question 26

What does (x:xs) do when defining a function?

Answer 26

Splits the input list into to variables the head, x, (first item) and the tail, xs, (the remaining items).

Question 27

What is a partial function?

Answer 27

A function that only works for some inputs and may crash or fail for others.

Question 28

Give an example of a partial function:

Answer 28

Head E.g. head [ ] There are no items in the list so the function crashes as it cannot return a head

Question 29

What is a total function?

Answer 29

A function that can handle all possible input and won’t crash.

Question 30

What is partial application?

Answer 30

Hard coding some of the arguments into a function e.g. add4(x) = 4+x