/in/foo.cc: In member function 'PolyList PolyList::operator+(const PolyList&)':
/in/foo.cc:27:28: error: passing 'const PolyList' as 'this' argument discards qualifiers [-fpermissive]
   p.m_sum = m_sum + p.ASum();
                            ^
/in/foo.cc:38:6: note:   in call to 'int PolyList::ASum()'
  int ASum()
      ^~~~
/in/foo.cc:27:28: error: assignment of member 'PolyList::m_sum' in read-only object
   p.m_sum = m_sum + p.ASum();
                            ^