Paul Lessing

I managed to simplify @derekrjones's approach a little so it only needs two types: ```ts type ValidFunction = unknown[] extends Arguments ? unknown extends ReturnType ? never : ((...args: Arguments)...

@tom-sherman I believe the issue is that using `unknown` in the input arguments is actually acting as a strict requirement, rather than a "I don't know what this will be"...

No, you're not missing anything - I missed that. 🤦 I'll have another look when I next get time, sorry!