commit 32f76f7ff does not take into account `AST_SymbolFunarg` is also `AST_SymbolVar`, so don't need to call `AST_Scope.def_variable()` twice
commit 32f76f7ff does not take into account `AST_SymbolFunarg` is also `AST_SymbolVar`, so don't need to call `AST_Scope.def_variable()` twice