public override VariableType CodeGen(CodeGenPass pass)
{
AST ast = Expr;
while (ast != null)
{
VariableType type = ast.CodeGen(pass);
if (type != null)
{
// 表达式的值依然在栈中，要pop出去
pass.Constructor.AddPop(type);
}
ast = ast.SiblingAST;
}
return(null);
}