Inheriting from a type containing instances of itself

[KerryC]

It doesn't seem to me that it is just a limitation of echo.

This fails with Error: attempting to call undeclared routine: 'ext=': 
    
    
    n0.children[0].ext = true
    
    
    Run

Whereas this works: 
    
    
    ExtNode(n0.children[0]).ext = true
    echo n1[]
    
    
    Run

Outputting (ext: true, children: ...)

Thanks everyone for the discussion on this!