# ECE 522 Assignment 1 – Exploring Programming Language Concepts solution

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## Description

1. Provide a common definition of functional programming.
2. 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
let newTotal = oldTotal + i
writeIORef totalRef \$! newTotal
loop \$! i + 1
loop 1
putStrLn \$ “The total is ” ++ show total
3. “Immutability is preferable over mutability”. Explain why this is normally considered correct.
4. Consider the following (pseudo-) machine code:
mov R1, \$y
mov R2, \$z
mov \$x, R3
a. Write the equivalent code in C.
b. Write the equivalent code in Haskell. (Hint: The code is a single line of code.)
c. Since this code is mutable in both C and Haskell, what does it imply for ALL languages?
5. 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 =
1
ECE 522 | Software Construction, Verification and Evolution
list
|> Seq.map sqrtx
|> Seq.sum
a. What does each function (imperativefun and functionalfun) do in the previous code?
b. 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.
c. Utilize the sqrtx function in Q5 to write a function which raises its argument to the 4
th power.
6. 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;
indicate 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
● Math.random()
7. Based on the definition of functionalfun presented in Q5, write a function in Rust that takes a
number x and returns . Also the function should be separate from the main function.
𝑖=1
𝑥
∑ 𝑖
2
+ 2
8. Write a Rust function that computes the volume of a sphere, given its radius. Again, this function
should be separate from the main function.
9. 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)))
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ECE 522 | Software Construction, Verification and Evolution
(else (+ 1 (x (cdr lis))))))
(else (+ (x (car lis)) (x (cdr lis))))))
10. 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.
a. 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)
b. 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));
}
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