first pieces

src/tool/GenerateAST.java

@@ -0,0 +1,69 @@
+package tool;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.nio.charset.Charset;
+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, Charset.defaultCharset());
+
+    writer.println("package lox;");
+    writer.println();
+    writer.println("import java.util.List;");
+    writer.println();
+    writer.println("abstract class " + baseName + " {");
+
+    for (String type : types) {
+      String className = type.split(":")[0].trim();
+      String fields = type.split(":")[1].trim();
+      defineType(writer, baseName, className, fields);
+    }
+
+    writer.println("}");
+    writer.close();
+  }
+
+  private static void defineType(
+      PrintWriter writer, String baseName, String className, String fieldList) {
+    writer.println("  static class " + className + " extends " + baseName + " {");
+
+    writer.println("    " + className + "(" + fieldList + ") { ");
+
+    String[] fields = fieldList.split(", ");
+    for (String field : fields) {
+      String name = field.split(" ")[1];
+      writer.println("      this." + name + " = " + name + ";");
+    }
+
+    writer.println("    }");
+    writer.println();
+
+    for (String field : fields) {
+      writer.println("    final " + field + ";");
+    }
+
+    writer.println("  }");
+    writer.println();
+  }
+}