function void
ast_remove(AST *node){
  AST_Parent *l = node->parent;
  assert(l);
  if (l->first==l->last){
    assert(node==l->last);
    l->first=l->last=0;
  }
  else if (l->last==node){
    l->last=l->last->prev;
    l->last->next=0;
  }
  else if (l->first==node){
    l->first=l->first->next;
    l->first->prev=0;
  }
  else {
    node->prev->next=node->next;
    node->next->prev=node->prev;
  }
  node->parent=0;
  node->prev=0;
  node->next=0;
}

function void
ast_push_last(AST_Parent *l, AST *node){
  if (l->first==0){
    l->first=l->last=node;
    node->prev=0;
    node->next=0;
  }
  else {
    l->last->next=node;
    node->prev=l->last;
    node->next=0;
    l->last=node;
  }
  node->parent=l;
}

function void
ast_push_first(AST_Parent *l, AST *node){
  if(l->first == 0){
    l->first = l->last = node;
    node->prev = 0;
    node->next = 0;
  }
  else {
    node->next = l->first;
    l->first->prev = node;
    node->prev = 0;
    l->first = node;
  }
  node->parent = l;
}

function void
ast_push_after(AST *in_list, AST *node){
  AST_Parent *parent = in_list->parent;
  assert(parent);
  assert(parent->first && parent->last);

  node->prev = in_list;
  if(in_list == parent->last){
    in_list->next = node;
    parent->last = node;
  }
  else {
    node->next = in_list->next;
    in_list->next = node;
    node->next->prev = node;
  }
  node->parent=parent;
}

function void
ast_push_before(AST *in_list, AST *node){
  AST_Parent *parent = in_list->parent;
  assert(parent);
  assert(parent->first && parent->last);

  node->next = in_list;
  if(parent->first == in_list){
    in_list->prev = node;
    parent->first = node;
  }
  else{
    node->prev = in_list->prev;
    in_list->prev = node;
    node->prev->next = node;
  }
  node->parent = parent;
}