[Oberon] Module aliases - what is the correct way to handle them

[Andreas Pirklbauer]

Here is one possible way to handle import aliases, as currently used in Extended Oberon.
Other possible variants (either more or less restrictive) do exist, of course.

  PROCEDURE ThisModule(name, orgname: ORS.Ident; decl: BOOLEAN; key: LONGINT): Object;
    VAR mod: Module; obj, obj1: Object;
  BEGIN obj1 := topScope; obj := obj1.next;  (*search for module*)
    WHILE (obj # NIL) & (obj(Module).orgname # orgname) DO obj1 := obj; obj := obj1.next END ;
    IF obj = NIL THEN  (*new module, search for alias*)
      obj := topScope.next;
      WHILE (obj # NIL) & (obj.name # name) DO obj := obj.next END ;
      IF obj = NIL THEN (*insert new module*)
        NEW(mod); mod.class := Mod; mod.rdo := FALSE;
        mod.name := name; mod.orgname := orgname; mod.val := key;
        mod.lev := nofmod; INC(nofmod); mod.type := noType; mod.dsc := NIL; mod.next := NIL;
        obj1.next := mod; obj := mod
      ELSIF decl THEN
        IF obj.rdo THEN ORS.Mark("mult def") ELSE ORS.Mark("invalid import order") END
      ELSE ORS.Mark("conflict with alias")
      END
    ELSIF decl THEN (*module already present, explicit import by declaration*)
      IF obj.rdo THEN ORS.Mark("mult def") ELSE ORS.Mark("invalid import order") END
    END ;
    RETURN obj
  END ThisModule;

Sample test suite with the expected error messages in a set of possible usage scenarios:

  http://github.com/andreaspirklbauer/Oberon-test-module-aliases/blob/master/Sources/TestAliases.Mod