std.sumtype?

[ryuukk_]

I'm not a fan of the syntax.. why is it a library instead of a 
language feature?..

```
Fahrenheit toFahrenheit(Temperature t)
{
     return Fahrenheit(
         t.match!(
             (Fahrenheit f) => f.degrees,
             (Celsius c) => c.degrees * 9.0/5 + 32,
             (Kelvin k) => k.degrees * 9.0/5 - 459.4
         )
     );
}
```

vs

```
Fahrenheit toFahrenheit(Temperature t)
{
     return match(t) {
             (Fahrenheit f) => f.degrees,
             (Celsius c) => c.degrees * 9.0/5 + 32,
             (Kelvin k) => k.degrees * 9.0/5 - 459.4
     };
}
```

I don't understand why make things confusing when it can be done 
simpler

Discriminated union should be a language feature, not lib!

Because now you depend on ``std``