Representing code chapter
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src/lox/AstPrinter.java
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42
src/lox/AstPrinter.java
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package lox;
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public class AstPrinter implements Expr.Visitor<String> {
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String print(Expr expr) {
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return expr.accept(this);
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}
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@Override
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public String visitBinaryExpr(Expr.Binary expr) {
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return parethesize(expr.operator.lexeme,
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expr.left, expr.right);
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}
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@Override
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public String visitGroupingExpr(Expr.Grouping expr) {
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return parethesize("group", expr.expression);
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}
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@Override
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public String visitLiteralExpr(Expr.Literal expr) {
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if (expr.value == null) return "nil";
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return expr.value.toString();
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}
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@Override
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public String visitUnaryExpr(Expr.Unary expr) {
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return parethesize(expr.operator.lexeme, expr.right);
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}
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private String parethesize(String name, Expr... exprs) {
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StringBuilder builder = new StringBuilder();
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builder.append("(").append(name);
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for (Expr expr : exprs) {
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builder.append(" ");
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builder.append(expr.accept(this));
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}
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builder.append(")");
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return builder.toString();
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}
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}
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68
src/lox/Expr.java
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68
src/lox/Expr.java
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package lox;
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import java.util.List;
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abstract class Expr {
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interface Visitor<R> {
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R visitBinaryExpr(Binary expr);
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R visitGroupingExpr(Grouping expr);
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R visitLiteralExpr(Literal expr);
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R visitUnaryExpr(Unary expr);
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}
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static class Binary extends Expr {
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Binary(Expr left, Token operator, Expr right) {
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this.left = left;
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this.operator = operator;
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this.right = right;
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}
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@Override
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<R> R accept(Visitor<R> visitor) {
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return visitor.visitBinaryExpr(this);
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}
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final Expr left;
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final Token operator;
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final Expr right;
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}
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static class Grouping extends Expr {
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Grouping(Expr expression) {
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this.expression = expression;
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}
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@Override
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<R> R accept(Visitor<R> visitor) {
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return visitor.visitGroupingExpr(this);
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}
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final Expr expression;
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}
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static class Literal extends Expr {
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Literal(Object value) {
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this.value = value;
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}
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@Override
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<R> R accept(Visitor<R> visitor) {
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return visitor.visitLiteralExpr(this);
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}
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final Object value;
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}
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static class Unary extends Expr {
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Unary(Token operator, Expr right) {
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this.operator = operator;
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this.right = right;
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}
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@Override
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<R> R accept(Visitor<R> visitor) {
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return visitor.visitUnaryExpr(this);
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}
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final Token operator;
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final Expr right;
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}
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abstract <R> R accept(Visitor<R> visitor);
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}
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96
src/tool/GenerateAst.java
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96
src/tool/GenerateAst.java
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package tool;
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import java.io.FileNotFoundException;
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import java.io.PrintWriter;
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import java.io.UnsupportedEncodingException;
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import java.util.Arrays;
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import java.util.List;
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public class GenerateAst {
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public static void main(String[] args) throws FileNotFoundException, UnsupportedEncodingException {
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if (args.length != 1) {
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System.err.println("Usage: generate_ast <output directory>");
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System.exit(64);
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}
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String outputDir = args[0];
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defineAst(outputDir, "Expr", Arrays.asList(
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"Binary : Expr left, Token operator, Expr right",
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"Grouping : Expr expression",
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"Literal : Object value",
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"Unary : Token operator, Expr right"
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));
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}
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private static void defineAst(
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String outputDir, String baseName, List<String> types) throws FileNotFoundException, UnsupportedEncodingException {
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String path = outputDir + "/" + baseName + ".java";
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PrintWriter writer = new PrintWriter(path, "UTF-8");
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writer.println("package lox;");
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writer.println();
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writer.println("import java.util.List;");
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writer.println();
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writer.println("abstract class " + baseName + " {");
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defineVisitor(writer, baseName, types);
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for (String type : types) {
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String className = type.split(":")[0].trim();
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String fields = type.split(":")[1].trim();
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defineType(writer, baseName, className, fields);
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}
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writer.println();
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writer.println("\tabstract <R> R accept(Visitor<R> visitor);");
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writer.println("}");
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writer.close();
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}
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private static void defineVisitor(
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PrintWriter writer, String baseName, List<String> types) {
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writer.println("\tinterface Visitor<R> {");
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for (String type : types) {
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String typeName = type.split(":")[0].trim();
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writer.println("\t\tR visit" + typeName + baseName + "(" +
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typeName + " " + baseName.toLowerCase() + ");");
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}
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writer.println("\t}");
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}
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private static void defineType(
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PrintWriter writer, String baseName,
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String className, String fieldList) {
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writer.println("\tstatic class " + className + " extends " + baseName + " {");
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writer.println("\t\t" + className + "(" + fieldList + ") {");
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String[] fields = fieldList.split(", ");
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for (String field : fields) {
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String name = field.split(" ")[1];
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writer.println("\t\t\tthis." + name + " = " + name + ";");
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}
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writer.println("\t\t}");
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writer.println();
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writer.println("\t\t@Override");
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writer.println("\t\t<R> R accept(Visitor<R> visitor) {");
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writer.println("\t\t\treturn visitor.visit" +
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className + baseName + "(this);");
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writer.println("\t\t}");
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writer.println();
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for (String field : fields) {
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writer.println("\t\tfinal " + field + ";");
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}
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writer.println("\t}");
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}
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}
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