/// <summary>Given the contents of case statement like `matchCode` or
/// `switch`, this method gets a list of the cases.</summary>
/// <returns>The first item in each pair is a list of the cases associated
/// with a single handler (for `default:`, the list is empty). The second
/// item is the handler code.</returns>
static internal VList <Pair <LNodeList, LNodeList> > GetCases(LNodeList body, IMessageSink sink)
{
var pairs = VList <Pair <LNodeList, LNodeList> > .Empty;
for (int i = 0; i < body.Count; i++)
{
bool isDefault;
if (body[i].Calls(S.Lambda, 2))
{
var alts = body[i][0].WithoutOuterParens().AsList(S.Tuple).SmartSelect(UnwrapBraces);
pairs.Add(Pair.Create(alts, body[i][1].AsList(S.Braces)));
}
else if ((isDefault = IsDefaultLabel(body[i])) || body[i].CallsMin(S.Case, 1))
{
var alts = isDefault ? LNodeList.Empty : body[i].Args.SmartSelect(UnwrapBraces);
int bodyStart = ++i;
for (; i < body.Count && !IsDefaultLabel(body[i]) && !body[i].CallsMin(S.Case, 1); i++)
{
}
var handler = new LNodeList(body.Slice(bodyStart, i - bodyStart));
pairs.Add(Pair.Create(alts, handler));
i--; // counteract i++ when loop repeats (redo)
}
else
{
Reject(sink, body[i], "expected 'case _:' or '_ => _'");
break;
}
}
return(pairs);
}