处理器无疑是计算机中最重要的部件,但并不是唯一的部件 。一台计算机也需要随机访 问存储器(R A M)来存放机器码指令以便让处理器执行。计算机还必须有一些方法使这些指 令进入R A M(输入设备)以及一些方法使程序执行结果得以看见(输出设备)。前面讲过, R A M是易失性的,当断电时,它的内容就会丢失。所以计算机中另一个有用的部件是永久存 储设备,当计算机断电的时候,它们可以保存代码和数据
Function of a Parser Takes the sequence of tokens produced by the scanner as its input and produces the syntax tree as its output. Parser Sequence of tokens Syntax-Tree
Basic antenna operation Receiving and transmitting antennas are identical: Time just flows in opposite directions. Antenna problems are solved knowing the current distribution J(x') in the antenna and using a vector potential
Main idea LL(1) Parsing uses an explicit stack rather than recursive calls to perform a parse An example: – a simple grammar for the strings of balanced parentheses: S→(S) S∣ε The following table shows the actions of a topdown parser given this grammar and the string ( )