pub fn lower(s: &str) -> String {
s.to_lowercase()
}
pub fn upper(s: &str) -> String {
s.to_uppercase()
}
pub fn reverse(s: &str) -> String {
s.chars().rev().collect()
}
pub fn length(s: &str) -> String {
s.len().to_string()
}
pub fn remove_whitespace(s: &str) -> String {
return s.split_whitespace().collect();
}