As part of a Roslyn code fix, I need to implement an interface on a class, if the class does not already implement it.

So far I'm able to detect whether the class implements the interface:

```
var implements = false;
foreach (var b in t.BaseList.Types)
{
    var name = (b.Type as IdentifierNameSyntax)?.Identifier.ValueText;
    if (name == "IInterfaceName")
    {
        implements = true;
        break;
    }
}

```

Now, if `implements` is false, I need to add the interface to the list of basetypes.
I've tried `t.BaseTypes.Add(...)` and here I'm a bit stuck - not sure how to construct the right parameter.

Is this the right approach?