docs: def n_exec_stmt(self, node):
          """
          exec_stmt ::= EXEC expr
          exec_stmt ::= EXEC expr IN test
          exec_stmt ::= EXEC expr IN test COMMA test
          """
          self.write(self.indent, 'exec ')
          self.preorder(node[1])
  
          if len(node) > 2:
              self.write(self.indent, ' in ')
              self.preorder(node[3])
              if len(node) > 5:
                  self.write(self.indent, ', ')
                  self.preorder(node[5])
          self.println()
          self.prune()