docs: def emit(self, ast_reg, ast_guide):
          ''' Default emit method: visit both ASTs and return the codegen '''
          if (ast_reg):
              self.visit(ast_reg)
          codegen_reg = self.codegen
          self.codegen = self.cg_type()
          if (ast_guide):
              self.visit(ast_guide)
          return (codegen_reg, self.codegen)