fixing get_package_names

Author: mmatera

mathics/builtin/system.py

@@ -230,13 +230,13 @@ class Packages(Predefined):
     </dl>
 
     X> $Packages
-    = {CombinatoricaOld`,ImportExport`,Internal`,System`,XML`}
+    = {CombinatoricaOld`,ImportExport`,XML`,Internal`,System`,Global`}
     #> MemberQ[$Packages, "System`"]
     = True
     """
 
     name = "$Packages"
-    rules = {'$Packages': '{"CombinatoricaOld`","ImportExport`","Internal`","System`","XML`"}',}
+    rules = {'$Packages': '{"CombinatoricaOld`", "ImportExport`",  "XML`","Internal`", "System`", "Global`"}',}
     # def evaluate(self, evaluation):
     #    return Expression(
     #        "List",

mathics/core/definitions.py

@@ -389,8 +389,13 @@ def lookup_name(self, name) -> str:
         return with_context
 
     def get_package_names(self) -> typing.List[str]:
-        # TODO: load from $Packages...
-        pass
+        packages = self.get_ownvalue("System`$Packages")
+        packages = packages.replace
+        assert packages.has_form("System`List", None)
+        packages = [c.get_string_value() for c in packages.leaves]
+        return packages
+
+
 
         #return sorted({name.split("`")[0] for name in self.get_names()})