5.3

Makefile

@@ -3,6 +3,10 @@
 
 build:
 	javac -d build/classes src/com/craftinginterpreters/lox/*
+	javac -d build/classes src/com/craftinginterpreters/tool/*
 
-run:
+lox:
 	java -cp build/classes com.craftinginterpreters.lox.Lox
+	
+gen-ast:
+	java -cp build/classes com.craftinginterpreters.tool.GenerateAst ./src/com/craftinginterpreters/lox

src/com/craftinginterpreters/lox/Expr.java

@@ -1,15 +1,68 @@
 package com.craftinginterpreters.lox;
 
+import java.util.list;
+
 abstract class Expr {
+	interface Visitor<R> {
+		R visitBinaryExpr(Binary expr);
+		R visitGroupingExpr(Grouping expr);
+		R visitLiteralExpr(Literal expr);
+		R visitUnaryExpr(Unary expr);
+	}
   static class Binary extends Expr {
     Binary(Expr left, Token operator, Expr right) {
     this.left = left;
-            this.operator = operator;
-            this.right = right;
+    this.Token = Token;
+    this.Expr = Expr;
     }
 
-        final Expr left;
-        final Token operator;
-        final Expr right;
+	@Override
+	<R> R accept(Visitor<R> visitor) {
+		return visitor.visitBinaryExpr(this);
 	}
+
+    final Expr left = Expr left;
+    final  Token operator =  Token operator;
+    final  Expr right =  Expr right;
+  }
+  static class Grouping extends Expr {
+    Grouping(Expr expression) {
+    this.expression = expression;
+    }
+
+	@Override
+	<R> R accept(Visitor<R> visitor) {
+		return visitor.visitGroupingExpr(this);
+	}
+
+    final Expr expression = Expr expression;
+  }
+  static class Literal extends Expr {
+    Literal(Object value) {
+    this.value = value;
+    }
+
+	@Override
+	<R> R accept(Visitor<R> visitor) {
+		return visitor.visitLiteralExpr(this);
+	}
+
+    final Object value = Object value;
+  }
+  static class Unary extends Expr {
+    Unary(Token operator, Expr right) {
+    this.operator = operator;
+    this.Expr = Expr;
+    }
+
+	@Override
+	<R> R accept(Visitor<R> visitor) {
+		return visitor.visitUnaryExpr(this);
+	}
+
+    final Token operator = Token operator;
+    final  Expr right =  Expr right;
+  }
+
+	abstract <R> R accept(Visitor<R> visitor);
 }

src/com/craftinginterpreters/tool/GenerateAst.java

@@ -30,6 +30,8 @@ public class GenerateAst {
         writer.println();
         writer.println("abstract class " + baseName + " {");
 
+        defineVisitor(writer, baseName, types);
+
         // The AST classes
         for (String type : types) {
             String className = type.split(":")[0].trim();
@@ -37,9 +39,23 @@ public class GenerateAst {
             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) {
@@ -57,6 +73,13 @@ public class GenerateAst {
 
         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) {