!7

concept TheList {
  S name;
  new L<S> entries;
  void add(S entry) { entries.add(entry); change(); }
}
concept Selection { TheList list; }
static TheList list; // cache of the above

p {
  dbIndexing(TheList, 'name);
  if ((list = uniq(Selection).list) == null) selectList("cool things");
  botIfMain();
}

synchronized answer {
  if "select *" { selectList($1); ret "OK, has " + n(list.entries, "entry"); }
  if "which" ret list.name;
  if "add *" { list.add($1); ret "OK, has position " + l(list.entries); }
  if "add * at *" { int i = parseInt($2)-1; list.entries.add(i, $1); list.change(); ret "OK"; }
  if "remove *" {
    int i = list.entries.indexOf($1); if (i < 0) ret "Not in list";
    list.entries.remove(i); list.change(); ret "OK, removed from position " + (i+1);
  }
  if "length" ret lstr(list.entries);
  if "entry *" { S x = get(list.entries, parseInt($1)-1); ret x == null ? "Nuttn" : "Entry: " + quote(x); }
  if "fix lol" { cset(lol(), entries := collect(list(TheList), 'name)); ret "OK"; }
}

svoid selectList(S name) {
  if (!hasConcept(TheList, +name)) lol().add(name);
  cset(uniq(Selection), list := list = uniq(TheList, +name));
}

// the "list of lists"
static TheList lol() { ret uniq(TheList, name := "lol"); }

static L<S> knownCommands() { ret findSupportedQuestionsInFunctions('answer); }

Began life as a copy of #1009226