call c.f() and become A()

[pirapira]

There is one case where reentrancy is fine, which is just before return.

Instead of doing

let x = c.f() reentrance {A ()};
return x and become A();

we could just say

call c.f() and become A();

This kind of sentences need to specify three things:

1. what to call
2. which state to use in the continuation and
3. what to return (the return value should not depend on the balance or the storage, which might have changed during the call).

Perhaps, we should just limit the use case to, just return what was returned from c.f().

[fordacious]

Could implement this as syntactic sugar (syntax transformation) as this is a special case. Assuming this is not too confusing to developers.