Add GenerateAst and AstPrinter

src/CMakeLists.txt

@@ -9,7 +9,10 @@ add_jar(Lox
   com/craftinginterpreters/lox/Lox.java
   com/craftinginterpreters/lox/TokenType.java
   com/craftinginterpreters/lox/Token.java
+  com/craftinginterpreters/lox/Expr.java
+  com/craftinginterpreters/lox/AstPrinter.java
   ENTRY_POINT com/craftinginterpreters/lox/Lox)
 
-get_target_property(_jarFile Lox JAR_FILE)
-get_target_property(_classDir Lox CLASSDIR)
+add_jar(GenerateAst
+  com/craftinginterpreters/tool/GenerateAst.java
+  ENTRY_POINT com/craftinginterpreters/tool/GenerateAst)

src/com/craftinginterpreters/lox/AstPrinter.java

@@ -0,0 +1,53 @@
+package com.craftinginterpreters.lox;
+
+/**
+ * AstPrinter
+ */
+class AstPrinter implements Expr.Visitor<String> {
+    String print(Expr expr) {
+        return expr.accept(this);
+    }
+
+    @Override
+    public String visitBinaryExpr(Expr.Binary expr) {
+        return parenthesize(expr.operator.lexeme, expr.left, expr.right);
+    }
+
+    @Override
+    public String visitGroupingExpr(Expr.Grouping expr) {
+        return parenthesize("group", expr.expression);
+    }
+
+    @Override
+    public String visitLiteralExpr(Expr.Literal expr) {
+        if (expr.value == null)
+            return "nil";
+        return expr.value.toString();
+    }
+
+    @Override
+    public 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();
+    }
+
+    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));
+    }
+}

src/com/craftinginterpreters/tool/GenerateAst.java

@@ -0,0 +1,88 @@
+package com.craftinginterpreters.tool;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.Arrays;
+import java.util.List;
+
+public class GenerateAst {
+    public static void main(String[] args) throws IOException {
+        if (args.length != 1) {
+            System.err.println("Usage: generate_ast <output directory>");
+            System.exit(64);
+        }
+
+        String outputDir = args[0];
+
+        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);
+
+        writer.println("package com.craftinginterpreters.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("  }");
+    }
+}