Define a romanNumberToInt function that converts a RomanNumber value, which is a list of Roman digits, into an integer. Hints: - Assume the Roman number representation is valid. - Use recursion to sum up number in romanNumber because it is a list. - Use pattern guards to manage case when digits come in reverse order, e. g. IX, IV.

Check the explanation

Explanation:

type RomanDigit = int

type RomanNumeral = RomanDigit list

type RomanDigit = I | V | X | L | C | D | M

type RomanNumeral = RomanNumeral of RomanDigit list

// / Converting a single RomanDigits to an integers here

let digitToInt =

function

| I - > 1

| V - > 5

| X - > 10

| L - > 50

| C - > 100

| D - > 500

| M - > 1000

/ / testing here

I |> digitToInt

V |> digitToInt

M |> digitToInt

let rec digitsToInt = function

/ / empty is notified by using 0

| [] - > 0

/ / special case when a smaller comes before larger

/ / convert both digits and add the difference to the sum

/ / Example: "IV" and "CM"

| smaller::larger::ns when smaller (digitToInt larger - digitToInt smaller) + digitsToInt ns

/ / otherwise convert the digit and add to the sum

| digit::ns - > digitToInt digit + digitsToInt ns

/ / tests

[I; I; I; I] |> digitsToInt

[I; V] |> digitsToInt

[V; I] |> digitsToInt

[I; X] |> digitsToInt

[M; C; M; L; X; X; I; X] |> digitsToInt / / that is 1979

[M; C; M; X; L; I; V] |> digitsToInt / / that is 1944

// / converts a RomanNumeral to an integer

let toInt (RomanNumeral digits) = digitsToInt digits

/ / test

let x = RomanNumeral [I; I; I; I]

x |> toInt

let x = RomanNumeral [M; C; M; L; X; X; I; X]

x |> toInt