[nem-en] recursive types

[Wiktor Zychla]

yet another question on pattern matching.

how do I tell the compiler that one of branches should have no code (return 
void)?

in following scenario:

public Foo( l : Lambda ) : void {
    match ( l ) {
        | Abs( ... ) => ...
        | App( ... ) => ...
        | _ => ????
    }
}

dropping the "_" branch at all causes the warning "matching non-exhaustive". 
to eliminate the warning I guess I need to put something there.

since I expect the match body to return void, I need to put something in 
place of ????.

putting the the junk there helps:

public Foo( l : Lambda ) : void {
    match ( l ) {
        | Abs( ... ) => ...
        | App( ... ) => ...
        | _ => mutable i = 0; i=1;
    }
}

but this in not a solution. could you provide a more elegant one?

interestingly, dropping the "=> body" causes somewhat misleading error:

public Foo( l : Lambda ) : void {
    match ( l ) {
        | Abs( ... ) => ...
        | App( ... ) => ...
        | _
    }
}

"found junk after pattern"

;)

actually the expected message would be rather "did not find anything after 
pattern".

Wiktor