Allow circular references in type aliases

[ghost]

Building on a question I asked on StackOverlow, I was wondering if it would be a nice addition if it would be possible to define types recursively. If I am guessing correctly this wouldn't be too difficult to implement.

Example:

type Document = [number | string | Array<Document>]

Currently, according to the spec, only classes and interfaces are allowed to reference themselves. Is there a reason for this?

Classes and interfaces can reference themselves in their internal structure...

[malibuzios]

Here are two related issues: #3496, #6230

[mhegazy]

As @malibuzios noted, looks like a duplicate of #6230