add scopes

src/lox/ASTPrinter.java

@@ -33,6 +33,11 @@ class ASTPrinter implements Expr.Visitor<String> {
     return expr.name.toString();
   }
 
+  @Override
+  public String visitAssignExpr(Expr.Assign expr) {
+    return expr.name.toString();
+  }
+
   private String parenthesize(String name, Expr... exprs) {
     StringBuilder builder = new StringBuilder();
 

src/lox/Environment.java

@@ -4,16 +4,44 @@ import java.util.HashMap;
 import java.util.Map;
 
 class Environment {
+  final Environment enclosing;
   private final Map<String, Object> values = new HashMap<>();
 
+  Environment() {
+    enclosing = null;
+  }
+
+  Environment(Environment enclosing) {
+    this.enclosing = enclosing;
+  }
+
   void define(String name, Object value) {
     values.put(name, value);
   }
 
+  void assign(Token name, Object value) {
+    if (values.containsKey(name.lexeme)) {
+      values.put(name.lexeme, value);
+      return;
+    }
+
+    if (enclosing != null) {
+      enclosing.assign(name, value);
+      return;
+    }
+
+    throw new RuntimeError(name, "Undefined variable '" + name.lexeme + "'.");
+  }
+
   Object get(Token name) {
     if (values.containsKey(name.lexeme)) {
       return values.get(name.lexeme);
     }
+
+    if (enclosing != null) {
+      return enclosing.get(name);
+    }
+
     throw new RuntimeError(name, "Undefined variable '" + name.lexeme + "'.");
   }
 }

src/lox/Expr.java

@@ -1,7 +1,10 @@
 package lox;
 
+import java.util.List;
+
 abstract class Expr {
   interface Visitor<R> {
+    R visitAssignExpr(Assign expr);
     R visitBinaryExpr(Binary expr);
     R visitGroupingExpr(Grouping expr);
     R visitLiteralExpr(Literal expr);
@@ -9,6 +12,21 @@ abstract class Expr {
     R visitVariableExpr(Variable expr);
   }
 
+  static class Assign extends Expr {
+    Assign(Token name, Expr value) {
+      this.name = name;
+      this.value = value;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitAssignExpr(this);
+    }
+
+    final Token name;
+    final Expr value;
+  }
+
   static class Binary extends Expr {
     Binary(Expr left, Token operator, Expr right) {
       this.left = left;

src/lox/Interpreter.java

@@ -89,6 +89,13 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
     return environment.get(expr.name);
   }
 
+  @Override
+  public Object visitAssignExpr(Expr.Assign expr) {
+    Object value = evaluate(expr.value);
+    environment.assign(expr.name, value);
+    return value;
+  }
+
   @Override
   public Void visitExpressionStmt(Stmt.Expression stmt) {
     evaluate(stmt.expression);
@@ -112,6 +119,12 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
     return null;
   }
 
+  @Override
+  public Void visitBlockStmt(Stmt.Block stmt) {
+    executeBlock(stmt.statements, new Environment(environment));
+    return null;
+  }
+
   private void checkNumberOperand(Token operator, Object operand) {
     if (operand instanceof Double) {
       return;
@@ -167,4 +180,18 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
   private void execute(Stmt stmt) {
     stmt.accept(this);
   }
+
+  void executeBlock(List<Stmt> statements, Environment environment) {
+    Environment previous = this.environment;
+    try {
+      this.environment = environment;
+
+      for (Stmt statement : statements) {
+        // could also just redesign this to accept an environment field everywhere
+        execute(statement);
+      }
+    } finally {
+      this.environment = previous;
+    }
+  }
 }

src/lox/Parser.java

@@ -50,6 +50,9 @@ class Parser {
     if (match(PRINT)) {
       return printStatement();
     }
+    if (match(LEFT_BRACE)) {
+      return new Stmt.Block(block());
+    }
     return expressionStatement();
   }
 
@@ -65,8 +68,35 @@ class Parser {
     return new Stmt.Expression(value);
   }
 
+  private List<Stmt> block() {
+    List<Stmt> statements = new ArrayList<>();
+
+    while (!check(RIGHT_BRACE) && !isAtEnd()) {
+      statements.add(declaration());
+    }
+    consume(RIGHT_BRACE, "Expect '}' after block.");
+    return statements;
+  }
+
+  private Expr assignment() {
+    Expr expr = equality();
+
+    if (match(EQUAL)) {
+      Token equals = previous();
+      Expr value = assignment();
+
+      if (expr instanceof Expr.Variable) {
+        Token name = ((Expr.Variable)expr).name;
+        return new Expr.Assign(name, value);
+      }
+      // does not throw because parsing _can_ continue
+      error(equals, "Invalid assignment target.");
+    }
+    return expr;
+  }
+
   private Expr expression() {
-    return equality();
+    return assignment();
   }
 
   private Expr equality() {

src/lox/Stmt.java

@@ -1,12 +1,28 @@
 package lox;
 
+import java.util.List;
+
 abstract class Stmt {
   interface Visitor<R> {
+    R visitBlockStmt(Block stmt);
     R visitExpressionStmt(Expression stmt);
     R visitVarStmt(Var stmt);
     R visitPrintStmt(Print stmt);
   }
 
+  static class Block extends Stmt {
+    Block(List<Stmt> statements) {
+      this.statements = statements;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitBlockStmt(this);
+    }
+
+    final List<Stmt> statements;
+  }
+
   static class Expression extends Stmt {
     Expression(Expr expression) {
       this.expression = expression;

src/tool/GenerateAST.java

@@ -1,5 +1,6 @@
 package tool;
 
+import java.io.File;
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.nio.charset.Charset;
@@ -17,6 +18,7 @@ public class GenerateAST {
         outputDir,
         "Expr",
         Arrays.asList(
+            "Assign   : Token name, Expr value",
             "Binary   : Expr left, Token operator, Expr right",
             "Grouping : Expr expression",
             "Literal  : Object value",
@@ -27,6 +29,7 @@ public class GenerateAST {
         outputDir,
         "Stmt",
         Arrays.asList(
+            "Block      : List<Stmt> statements",
             "Expression : Expr expression",
             "Var        : Token name, Expr initializer",
             "Print      : Expr expression"));
@@ -34,13 +37,13 @@ public class GenerateAST {
 
   private static void defineAST(String outputDir, String baseName, List<String> types)
       throws IOException {
-    String path = outputDir + "/" + baseName + ".java";
+    String path = outputDir + File.separator + baseName + ".java";
     PrintWriter writer = new PrintWriter(path, Charset.defaultCharset());
 
     writer.println("package lox;");
     writer.println();
-    //    writer.println("import java.util.List;");
+    writer.println("import java.util.List;");
-    //    writer.println();
+    writer.println();
     writer.println("abstract class " + baseName + " {");
 
     defineVisitor(writer, baseName, types);