Depends, are you talking about holes as in a type annotation that let’s the compiler help you figure out the type, or holes as in bugs or missing functionality?

Depends, are you talking about holes as in a type annotation that let’s the compiler help you figure out the type, or holes as in bugs or missing functionality? In the first case, no, but I see the utility and might add it in later. In the second case: probably. This is Alpha 1, after all, In the example you mention, Play would infer that the code places a Union on the stack, and would require a multi-word (pattern matching word) to deal with it later.