环境
- Time 2023-07-09
- Java 17
前言
说明
参考：
- https://craftinginterpreters.com/contents.html
- https://github.com/GuoYaxiang/craftinginterpreters_zh
- https://space.bilibili.com/44550904
目标
使用 Java 语言脚本来自动生成代码树。
GenerateAst
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.List;public class GenerateAst {public static void main(String[] args) throws IOException {// 根据实际情况，修改成对应的代码路径// String outputDir = "C:\\workspace\\demo\\src\\main\\java\\com\\example\\lox";defineAst(outputDir, "Expr", Arrays.asList("Binary : Expr left, Token operator, Expr right","Grouping : Expr expression","Literal : Object value","Unary : Token operator, Expr right"));}private static void defineAst(String outputDir, String baseName, List<String> types)throws IOException {String path = outputDir + "/" + baseName + ".java";PrintWriter writer = new PrintWriter(path, StandardCharsets.UTF_8);writer.println("package com.example.lox;");writer.println();writer.println("import java.util.List;");writer.println();writer.println("abstract class " + baseName + " {");defineVisitor(writer, baseName, types);for (String type : types) {String className = type.split(":")[0].trim();String fields = type.split(":")[1].trim();defineType(writer, baseName, className, fields);}// The base accept() method.writer.println();writer.println(" abstract <R> R accept(Visitor<R> visitor);");writer.println("}");writer.close();}private static void defineVisitor(PrintWriter writer, String baseName, List<String> types) {writer.println(" interface Visitor<R> {");for (String type : types) {String typeName = type.split(":")[0].trim();writer.println(" R visit" + typeName + baseName + "(" +typeName + " " + baseName.toLowerCase() + ");");}writer.println(" }");}private static void defineType(PrintWriter writer, String baseName,String className, String fieldList) {writer.println(" static class " + className + " extends " +baseName + " {");// Constructor.writer.println(" " + className + "(" + fieldList + ") {");// Store parameters in fields.String[] fields = fieldList.split(", ");for (String field : fields) {String name = field.split(" ")[1];writer.println(" this." + name + " = " + name + ";");}writer.println(" }");// Visitor pattern.writer.println();writer.println(" @Override");writer.println(" <R> R accept(Visitor<R> visitor) {");writer.println(" return visitor.visit" +className + baseName + "(this);");writer.println(" }");// Fields.writer.println();for (String field : fields) {writer.println(" final " + field + ";");}writer.println(" }");}
}
Expr
package com.example.lox;abstract class Expr {abstract <R> R accept(Visitor<R> visitor);interface Visitor<R> {R visitBinaryExpr(Binary expr);R visitGroupingExpr(Grouping expr);R visitLiteralExpr(Literal expr);R visitUnaryExpr(Unary expr);}static class Binary extends Expr {final Expr left;final Token operator;final Expr right;Binary(Expr left, Token operator, Expr right) {this.left = left;this.operator = operator;this.right = right;}@Override<R> R accept(Visitor<R> visitor) {return visitor.visitBinaryExpr(this);}}static class Grouping extends Expr {final Expr expression;Grouping(Expr expression) {this.expression = expression;}@Override<R> R accept(Visitor<R> visitor) {return visitor.visitGroupingExpr(this);}}static class Literal extends Expr {final Object value;Literal(Object value) {this.value = value;}@Override<R> R accept(Visitor<R> visitor) {return visitor.visitLiteralExpr(this);}}static class Unary extends Expr {final Token operator;final Expr right;Unary(Token operator, Expr right) {this.operator = operator;this.right = right;}@Override<R> R accept(Visitor<R> visitor) {return visitor.visitUnaryExpr(this);}}
}
AstPrinter
package com.example.lox;class AstPrinter implements Expr.Visitor<String> {public static void main(String[] args) {Expr expression = new Expr.Binary(new Expr.Unary(new Token(TokenType.MINUS, "-", null, 1),new Expr.Literal(123)),new Token(TokenType.STAR, "*", null, 1),new Expr.Grouping(new Expr.Literal(45.67)));System.out.println(new AstPrinter().print(expression));}String print(Expr expr) {return expr.accept(this);}@Overridepublic String visitBinaryExpr(Expr.Binary expr) {return parenthesize(expr.operator.lexeme,expr.left, expr.right);}@Overridepublic String visitGroupingExpr(Expr.Grouping expr) {return parenthesize("group", expr.expression);}@Overridepublic String visitLiteralExpr(Expr.Literal expr) {if (expr.value == null) return "nil";return expr.value.toString();}@Overridepublic String visitUnaryExpr(Expr.Unary expr) {return parenthesize(expr.operator.lexeme, expr.right);}private String parenthesize(String name, Expr... exprs) {StringBuilder builder = new StringBuilder();builder.append("(").append(name);for (Expr expr : exprs) {builder.append(" ");builder.append(expr.accept(this));}builder.append(")");return builder.toString();}
}
总结
实现了一个代码生成器，验证了代码生成器的功能。
