public override void Visit(Pass p, ExpressionUsage u = ExpressionUsage.Statement)
{
p.BeginScope(this);
for (var i = 0; i < Statements.Count; i++)
{
p.Next(this);
var s = Statements[i];
p.VisitNullable(ref s);
Statements[i] = s;
}
p.EndScope(this);
}