Description
- Provide a common definition of functional programming. (2 marks)
- Haskell is considered by many to be a pure functional programming language. Explain the following piece of Haskell code and discuss its relationship with the definition in Q. 1.
| import Data.IORef main :: IO () main = do
putStrLn “I’m going to calculate a sum, hang on a sec” totalRef <- newIORef (0 :: Int) let loop i | i > 100 = pure () | otherwise = do oldTotal <- readIORef totalRef let newTotal = oldTotal + i writeIORef totalRef $! newTotal loop $! i + 1 loop 1 total <- readIORef totalRef putStrLn $ “The total is ” ++ show total |
- “Immutability is preferable over mutability”. Explain why this is normally considered correct.
- Consider the following (pseudo-) machine code:
mov R1, $y mov R2, $z add R3, R1, R2
mov $x, R3
- Write the equivalent code in C.
- Write the equivalent code in Haskell.
- Since this code is mutable, what does it imply for ALL languages?
- Consider the following code in F#:
| let sqrtx x = x * x let imperativefun list = let mutable total = 0 for i in list do
let x = sqrtx i total <- total + x total let functionalfun list = list |> Seq.map sqrtx |> Seq.sum |
- What does each function do in the previous code?
- Consider a subset of ISO 9126
- Reliability
- Efficiency
- Maintainability
- Portability
Argue about the impact, if any, of the two different implementations (imperativefun and functionalfun) on these characteristics.
- Utilize the sqrtx function in Q5 to write a function which raises its argument to the 4th
- Pure functions: A pure function is a function that, given the same input, will always return the same output and does not have any observable side effect. Functional programming likes pure functions; which of the following are pure functions:
- changing the file system
- inserting a record into a database
- making an http call
- mutations
- printing to the screen / logging
- obtaining user input
- querying the DOM
- accessing system state
- random()
- Based on the definition of functionalfun presented in Q5, write a function in Rust that takes a number x and returns ∑𝑥𝑖=1𝑖2 + 2.
- Write a Rust function that computes the volume of a sphere, given its radius.
- What does the following Scheme function do?
(define (x lis)
(cond
((null? lis) 0)
((not (list? (car lis)))
(cond
((eq? (car lis) #f) (x (cdr lis)))
(else (+ 1 (x (cdr lis))))))
(else (+ (x (car lis)) (x (cdr lis))))
- Total functions state that, for every valid input value, there is a valid, terminating output value. In contrast to a total function, a partial function may result in an infinite loop, program crash, or runtime exception for some input.
- Explain what happens when you present the following Haskell code to its compiler
| data Colour = Red | Yellow | Blue
sayColour colour = case colour of Red -> “red” |
Yellow -> “yellow”
main = putStrLn (sayColour Blue)
- Explain what happens when you present the following Rust code to its compiler
enum Colour {
Red,
Yellow,
Blue,
}
fn say_colour(colour: &Colour) -> &’static str {
match colour { Colour::Red => “red”,
Colour::Yellow => “yellow”,
}
}
fn main() {
println!(“{}”, say_colour(&Colour::Blue)); }
