🚀 go-pugleaf

The fourth pass of the old ETH compiler had mutually importing internal
modules, both at the outer level of the enclosing implementation module.
As the compiler could compile itself, I am nonplussed that its compilers
derived from it could not.

I would note that if two internal modules are mutually importing, that both
may not have code in their module bodies (the initialization sections, not
procedures), as it is a case of circular initialization.  A degenerate
example might be

  MODULE A;
    MODULE B;
      IMPORT c;
      EXPORT b;
      VAR b : CARDINAL;
      BEGIN
        b := c + 42
        END B;
    MODULE C;
      IMPORT b;
      EXPORT c;
      VAR c : CARDINAL;
      BEGIN
        c := b + 42
        END C;
    END A.

randy