如何使用Java语言编写PL/0编译程序的语法分析程序
时间: 2023-11-25 11:07:19 浏览: 122
要使用Java语言编写PL/0编译程序的语法分析程序,需要遵循以下步骤:
1. 定义语法规则:根据PL/0语言的文法规则定义语法规则,可以使用BNF(巴克斯-诺尔范式)或EBNF(扩展巴克斯-诺尔范式)表示语法规则。
2. 构建语法分析器:使用Java语言编写语法分析器,可以使用自顶向下的递归下降分析法或自底向上的LR分析法。其中,递归下降分析法是最常见的语法分析方法。
3. 分析PL/0程序:将PL/0程序作为输入,使用语法分析器进行分析。如果程序符合语法规则,则输出语法树或抽象语法树,否则报错提示语法错误。
下面是一个简单的使用Java语言编写PL/0编译程序的语法分析程序的示例:
```java
import java.util.ArrayList;
import java.util.List;
public class Parser {
private Lexer lexer;
private Token currentToken;
public Parser(Lexer lexer) {
this.lexer = lexer;
currentToken = lexer.nextToken();
}
public void parse() {
program();
}
private void program() {
block();
match(TokenType.DOT);
}
private void block() {
if (currentToken.getType() == TokenType.CONST) {
constDeclaration();
}
if (currentToken.getType() == TokenType.VAR) {
varDeclaration();
}
while (currentToken.getType() == TokenType.PROCEDURE) {
procedureDeclaration();
}
statement();
}
private void constDeclaration() {
match(TokenType.CONST);
do {
match(TokenType.ID);
match(TokenType.EQ);
match(TokenType.NUM);
} while (currentToken.getType() == TokenType.COMMA);
match(TokenType.SEMI);
}
private void varDeclaration() {
match(TokenType.VAR);
do {
match(TokenType.ID);
} while (currentToken.getType() == TokenType.COMMA);
match(TokenType.SEMI);
}
private void procedureDeclaration() {
match(TokenType.PROCEDURE);
match(TokenType.ID);
match(TokenType.SEMI);
block();
match(TokenType.SEMI);
}
private void statement() {
if (currentToken.getType() == TokenType.ID) {
match(TokenType.ID);
match(TokenType.ASSIGN);
expression();
} else if (currentToken.getType() == TokenType.CALL) {
match(TokenType.CALL);
match(TokenType.ID);
} else if (currentToken.getType() == TokenType.BEGIN) {
match(TokenType.BEGIN);
statement();
while (currentToken.getType() == TokenType.SEMI) {
match(TokenType.SEMI);
statement();
}
match(TokenType.END);
} else if (currentToken.getType() == TokenType.IF) {
match(TokenType.IF);
condition();
match(TokenType.THEN);
statement();
if (currentToken.getType() == TokenType.ELSE) {
match(TokenType.ELSE);
statement();
}
} else if (currentToken.getType() == TokenType.WHILE) {
match(TokenType.WHILE);
condition();
match(TokenType.DO);
statement();
}
}
private void condition() {
expression();
if (currentToken.getType() == TokenType.EQ ||
currentToken.getType() == TokenType.NE ||
currentToken.getType() == TokenType.LT ||
currentToken.getType() == TokenType.LE ||
currentToken.getType() == TokenType.GT ||
currentToken.getType() == TokenType.GE) {
match(currentToken.getType());
expression();
}
}
private void expression() {
if (currentToken.getType() == TokenType.PLUS ||
currentToken.getType() == TokenType.MINUS) {
match(currentToken.getType());
}
term();
while (currentToken.getType() == TokenType.PLUS ||
currentToken.getType() == TokenType.MINUS) {
match(currentToken.getType());
term();
}
}
private void term() {
factor();
while (currentToken.getType() == TokenType.TIMES ||
currentToken.getType() == TokenType.SLASH) {
match(currentToken.getType());
factor();
}
}
private void factor() {
if (currentToken.getType() == TokenType.ID) {
match(TokenType.ID);
} else if (currentToken.getType() == TokenType.NUM) {
match(TokenType.NUM);
} else if (currentToken.getType() == TokenType.LPAREN) {
match(TokenType.LPAREN);
expression();
match(TokenType.RPAREN);
}
}
private void match(TokenType type) {
if (currentToken.getType() == type) {
currentToken = lexer.nextToken();
} else {
throw new RuntimeException("Unexpected token: " + currentToken.getValue());
}
}
}
```
在这个示例中,我们定义了PL/0语言的语法规则,并使用自顶向下的递归下降分析法编写了语法分析器,包括了program、block、constDeclaration、varDeclaration、procedureDeclaration、statement、condition、expression和factor等方法。我们使用Lexer类将PL/0程序转换为Token序列,并将其传递给Parser类进行语法分析。最后,我们在main方法中创建Lexer和Parser对象,将PL/0程序传递给Parser的parse方法进行语法分析。
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