sample.rs

    fn double_mapper_factory(tfm: fn(f64) -> f64) -> fn(&InterpLocalVars) -> Option<JvmValue> {
        |args: &InterpLocalVars| -> Option<JvmValue> {
            let d = match args.load(0) {
                JvmValue::Double { val: v } => v,
                x => panic!("Non-double value {} of type {} encountered in Math", x, x.name())
            };

            Some(JvmValue::Double {val: tfm(d)})
        }
    }