Function input_validated 

pub fn input_validated<S, V>(
    prompt: S,
    default: Option<&str>,
    validator: V,
) -> Result<String>
where
    S: Into<String>,
    V: Fn(&String) -> Result<(), &'static str> + Clone,

Prompt for text input with custom validation

Returns an error in non-interactive mode if no default is provided.