pub mod ui; pub enum Operator { Add, Sub, Mul, Div, } impl Operator { pub fn parse(c: char) -> Result { match c { '+' => Ok(Self::Add), '-' => Ok(Self::Sub), '*' => Ok(Self::Mul), '/' => Ok(Self::Div), _ => Err(ParseOperatorError(c)), } } } pub struct ParseOperatorError(char);