namespace Algorithms.Strings

type System.Char with

member this.IsUpper(): bool =

match this with

| c when c >= 'A' && c <= 'Z' -> true

| _ -> false

member this.IsLower(): bool =

match this with

| c when c >= 'a' && c <= 'z' -> true

| _ -> false

member this.Lower(): char =

match this with

| c when c >= 'A' && c <= 'Z' -> (char) ((int) this + 32)

| _ -> this

member this.Upper(): char =

match this with

| c when c >= 'a' && c <= 'z' -> (char) ((int) this - 32)

| _ -> this

/// <summary>

/// This function will convert all lowercase letters to uppercase letters and vice versa

/// </summary>

let swapCase (sentence: string): string =

let mutable newString = ""

for character in sentence do

match character with

| c when c.IsUpper() -> newString <- newString + (string) (character.Lower())

| c when c.IsLower() -> newString <- newString + (string) (character.Upper())

| _ -> newString <- newString + (string) character

newString