Recursively defined matcher function

[sighoya]

On Sunday, 3 January 2021 at 18:49:40 UTC, sighoya wrote:
> ```
> alias matcherSignature(T:matcherSignature!T) = T (T[] 
> matchers...);
> ```
>

Ahhh, I meant this:

```
alias matcherSignature(T:matcherSignature!T) = Matcher (T[]  
matchers...);
``

> I think we would require proper singleton types to model this 
> as:
>
> ```
> matcherSignature(matcherSignature.type[] matcherSignatures ...)
> ```

and this:

```
Matcher matcherSignature(matcherSignature.type[] 
matcherSignatures...)
```