Handling without control

It would be great if objects could be passed implicitly without introducing an effect handler.

```
interface State {
def get(): Int
def set(x: Int): Unit
}

def myComputation(): Int / State = do get()

def main() = {
var s = 0;
with State {
def get() = s
def set(x: Int) = s = x
};
myComputation()
}
```

The typing rule for `with` should be like

```
Γ |- b : F Γ |- s : 𝜏 / ε
――――――――――――――――――――――――――――――
Γ |- with b; s : 𝜏 / (ε - F)
```