Partial is similar to Option where
Fake contains a value of the right type that can be further used (e.g. in
and_then) but this value is a dummy value used to be able to compute the rest and detect more errors. For any method, we have the ordering:
Nothing; a Fake value will never be a Value again.
Use case: When compiling, an error in one function must be reported but should not prevent the compilation of a second function to detect more errors in one run. This intermediate state is represented by