public Span Span(SpanKind kind, params ISymbol[] symbols)
{
var builder = new SpanBuilder();
builder.Kind = kind;
foreach (var symbol in symbols)
{
builder.Accept(symbol);
}
var span = builder.Build();
if (_last != null)
{
span.Previous = _last;
_last.Next = span;
}
_last = span;
return span;
}