Shared via mypy Playground

main.py

# Run the type checking with "mypy --strict foo.py"

class Add(tuple[int,int]):
    pass

class Const(int):
    pass

Expr = Add | Const

def my_eval(e : Expr) -> int:
    match e:
        case Add((a,b)):
            return a + b
        case Const(x):
            return x

print(my_eval(Const(42)))
print(my_eval(Add((42,45))))