Define a function romanDigitToInt that converts a single Roman digit to a decimal integer. This function takes an argument as a element of the RomanDigit union type and transforms it into the decimal integer using patter matching. This function should have signature: RomanDigit - > int.

let convertRomanToInt romanNumber : int =

match romanNumber with

| 'I' - > 1

| 'V' - > 5

| 'X' - > 10

| 'L' - > 50

| 'C' - > 100

| 'D' - > 500

| 'M' - > 100

let rec romanNumberToInteger romanNumber =

if (String. length romanNumber = 1) then

convertRomanToInt romanNumber.[0]

elif (String. length romanNumber = 0) then 0

else let atuple = (romanNumber.[0], romanNumber.[1])

let f atuple = match atuple with

| (f, s) when (convertRomanToInt f) > = (convertRomanToInt s) - > (convertRomanToInt f) + (romanNumberToInteger romanNumber.[1 ... ])

| (f, s) when (convertRomanToInt f) (convertRomanToInt s) - (convertRomanToInt f) + (romanNumberToInteger romanNumber.[2 ... ])

f atuple

let charToRomanDigit c =

printfn "%c" c

match c with

| 'I' - > 'I'

| 'V' - > 'V'

| 'X' - > 'X'

| 'L' - > 'L'

| 'C' - > 'C'

| 'D' - > 'D'

| 'M' - > 'M'

| _ - > failwith "Invalid Entry"

let stringToNumber str =

let upperDigit (x:string) = x. ToUpper ()

let upperString = upperDigit str

printfn "%s" upperString

String. collect (fun c - > sprintf "%c" (charToRomanDigit c)) upperString

let romanNumber = "XIX"

let upperDigit (x:string) = x. ToUpper ()

printfn "a: %s" (upperDigit romanNumber)

romanNumber = stringToNumber romanNumber

printfn "/nValue = %d" (romanNumberToInteger romanNumber)

Explanation:

Create a function called convertRomanToInt for pattern matching to convert romanNumber to valid integer Create a recursive function called romanNumberToInteger and check if length of romanNumber is 1 or 0. Check whether the first character is less than second character, then its reverse otherwise it's normal. Create tuple of first and second character for pattern matching. Create a function charToRomanDigit and use String. collect to go through each character present in string and reconstruct them again. System. Char. ToUpper is used to convert a character to uppercase and stringToNumber to convert string in valid Roman number. Finally print the results.