examples/result/try/try.rs

mod checked {
    #[deriving(Show)]
    enum MathError {
        DivisionByZero,
        NegativeLogarithm,
        NegativeSquareRoot,
    }

    type MathResult = Result<f64, MathError>;

    fn div(x: f64, y: f64) -> MathResult {
        if y == 0.0 {
            Err(DivisionByZero)
        } else {
            Ok(x / y)
        }
    }

    fn sqrt(x: f64) -> MathResult {
        if x < 0.0 {
            Err(NegativeSquareRoot)
        } else {
            Ok(x.sqrt())
        }
    }

    fn ln(x: f64) -> MathResult {
        if x < 0.0 {
            Err(NegativeLogarithm)
        } else {
            Ok(x.ln())
        }
    }

    // Intermediate function
    fn op_(x: f64, y: f64) -> MathResult {
        // if `div` "fails", then `DivisionByZero` will be `return`ed
        let ratio = try!(div(x, y));

        // if `ln` "fails", then `NegativeLogarithm` will be `return`ed
        let ln = try!(ln(ratio));

        sqrt(ln)
    }

    pub fn op(x: f64, y: f64) {
        match op_(x, y) {
            Err(why) => fail!(match why {
                NegativeLogarithm => "logarithm of negative number",
                DivisionByZero => "division by zero",
                NegativeSquareRoot => "square root of negative number",
            }),
            Ok(value) => println!("{}", value),
        }
    }
}

fn main() {
    checked::op(1.0, 10.0);
}