Add break statement

src/com/craftinginterpreters/lox/AstPrinter.java

@@ -64,6 +64,11 @@ class AstPrinter implements Expr.Visitor<String>, Stmt.Visitor<String> {
         return builder.toString();
     }
 
+    @Override
+    public String visitBreakStmt(Stmt.Break statement) {
+        return "break";
+    }
+
     @Override
     public String visitPrintStmt(Stmt.Print statement) {
         return parenthesize("print", statement.expression);

src/com/craftinginterpreters/lox/Break.java

@@ -0,0 +1,5 @@
+package com.craftinginterpreters.lox;
+
+class Break extends RuntimeException {
+
+}

src/com/craftinginterpreters/lox/CMakeLists.txt

@@ -20,4 +20,5 @@ add_jar(Lox
   Interpreter.java
   RuntimeError.java
   Environment.java
+  Break.java
   ENTRY_POINT com/craftinginterpreters/lox/Lox)

src/com/craftinginterpreters/lox/Interpreter.java

@@ -161,13 +161,22 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
 
     @Override
     public Void visitWhileStmt(Stmt.While stmt) {
+        try {
             while (isTruthy(evaluate(stmt.condition))) {
                 execute(stmt.body);
             }
+        } catch (Break ex) {
+            // We continue on.
+        }
 
         return null;
     }
 
+    @Override
+    public Void visitBreakStmt(Stmt.Break stmt) {
+        throw new Break();
+    }
+
     @Override
     public Object visitAssignExpr(Expr.Assign expr) {
         Object value = evaluate(expr.value);

src/com/craftinginterpreters/lox/Parser.java

@@ -44,6 +44,8 @@ class Parser {
     }
 
     private Stmt statement() {
+        if (match(BREAK))
+            return breakStatement();
         if (match(FOR))
             return forStatement();
         if (match(IF))
@@ -84,13 +86,11 @@ class Parser {
         Stmt body = statement();
 
         if (increment != null) {
-            body = new Stmt.Block(
-                                  Arrays.asList(
-                                                body,
-                            new Stmt.Expression(increment)));
+            body = new Stmt.Block(Arrays.asList(body, new Stmt.Expression(increment)));
         }
 
-        if (condition == null) condition = new Expr.Literal(true);
+        if (condition == null)
+            condition = new Expr.Literal(true);
         body = new Stmt.While(condition, body);
 
         if (initializer != null) {
@@ -100,6 +100,11 @@ class Parser {
         return body;
     }
 
+    private Stmt breakStatement() {
+        consume(SEMICOLON, "Expect ';' after break statement.");
+        return new Stmt.Break();
+    }
+
     private Stmt ifStatement() {
         consume(LEFT_PAREN, "Expect '(' after 'if'.");
         Expr condition = expression();

src/com/craftinginterpreters/lox/Scanner.java

@@ -33,6 +33,7 @@ class Scanner {
         keywords.put("true", TRUE);
         keywords.put("var", VAR);
         keywords.put("while", WHILE);
+        keywords.put("break", BREAK);
     }
 
     Scanner(String source) {
@@ -54,16 +55,36 @@ class Scanner {
         char c = advance();
 
         switch (c) {
-        case '(': addToken(LEFT_PAREN); break;
-        case ')': addToken(RIGHT_PAREN); break;
-        case '{': addToken(LEFT_BRACE); break;
-        case '}': addToken(RIGHT_BRACE); break;
-        case ',': addToken(COMMA); break;
-        case '.': addToken(DOT); break;
-        case '-': addToken(MINUS); break;
-        case '+': addToken(PLUS); break;
-        case ';': addToken(SEMICOLON); break;
-        case '*': addToken(STAR); break;
+            case '(':
+                addToken(LEFT_PAREN);
+                break;
+            case ')':
+                addToken(RIGHT_PAREN);
+                break;
+            case '{':
+                addToken(LEFT_BRACE);
+                break;
+            case '}':
+                addToken(RIGHT_BRACE);
+                break;
+            case ',':
+                addToken(COMMA);
+                break;
+            case '.':
+                addToken(DOT);
+                break;
+            case '-':
+                addToken(MINUS);
+                break;
+            case '+':
+                addToken(PLUS);
+                break;
+            case ';':
+                addToken(SEMICOLON);
+                break;
+            case '*':
+                addToken(STAR);
+                break;
             case '!':
                 addToken(match('=') ? BANG_EQUAL : BANG);
                 break;
@@ -79,7 +100,8 @@ class Scanner {
             case '/':
                 if (match('/')) {
                     // A comment goes until the end of the line.
-                while (peek() != '\n' && !isAtEnd()) advance();
+                    while (peek() != '\n' && !isAtEnd())
+                        advance();
                 } else {
                     addToken(SLASH);
                 }
@@ -96,7 +118,9 @@ class Scanner {
                 line++;
                 break;
 
-        case '"': string(); break;
+            case '"':
+                string();
+                break;
 
             default:
                 if (isDigit(c)) {
@@ -111,34 +135,38 @@ class Scanner {
     }
 
     private void identifier() {
-        while (isAlphaNumeric(peek())) advance();
+        while (isAlphaNumeric(peek()))
+            advance();
 
         String text = source.substring(start, current);
         TokenType type = keywords.get(text);
-        if (type == null) type = IDENTIFIER;
+        if (type == null)
+            type = IDENTIFIER;
         addToken(type);
     }
 
     private void number() {
-        while (isDigit(peek())) advance();
+        while (isDigit(peek()))
+            advance();
 
         // Look for a fractional part.
         if (peek() == '.' && isDigit(peekNext())) {
             // Consume the "."
             advance();
 
-            while (isDigit(peek())) advance();
+            while (isDigit(peek()))
+                advance();
         }
 
-        addToken(NUMBER,
-                 Double.parseDouble(source.substring(start, current)));
+        addToken(NUMBER, Double.parseDouble(source.substring(start, current)));
     }
 
     // I guess we won't be able to include escaped characters in the string? At
     // least not escaped " characters.
     private void string() {
         while (peek() != '"' && !isAtEnd()) {
-            if (peek() == '\n') line++;
+            if (peek() == '\n')
+                line++;
             advance();
         }
 
@@ -156,27 +184,29 @@ class Scanner {
     }
 
     private boolean match(char expected) {
-        if (isAtEnd()) return false;
-        if (source.charAt(current) != expected) return false;
+        if (isAtEnd())
+            return false;
+        if (source.charAt(current) != expected)
+            return false;
 
         current++;
         return true;
     }
 
     private char peek() {
-        if (isAtEnd()) return '\0';
+        if (isAtEnd())
+            return '\0';
         return source.charAt(current);
     }
 
     private char peekNext() {
-        if (current + 1 >= source.length()) return '\0';
+        if (current + 1 >= source.length())
+            return '\0';
         return source.charAt(current + 1);
     }
 
     private boolean isAlpha(char c) {
-        return (c >= 'a' && c <= 'z') ||
-            (c >= 'A' && c <= 'Z') ||
-            c == '_';
+        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_';
     }
 
     private boolean isAlphaNumeric(char c) {

src/com/craftinginterpreters/lox/TokenType.java

@@ -2,19 +2,16 @@ package com.craftinginterpreters.lox;
 
 enum TokenType {
     // Single-character tokens.
-    LEFT_PAREN, RIGHT_PAREN, LEFT_BRACE, RIGHT_BRACE, COMMA, DOT, MINUS, PLUS,
-    SEMICOLON, SLASH, STAR,
+    LEFT_PAREN, RIGHT_PAREN, LEFT_BRACE, RIGHT_BRACE, COMMA, DOT, MINUS, PLUS, SEMICOLON, SLASH, STAR,
 
     // One or two character tokens.
-    BANG, BANG_EQUAL, EQUAL, EQUAL_EQUAL, GREATER, GREATER_EQUAL, LESS,
-    LESS_EQUAL,
+    BANG, BANG_EQUAL, EQUAL, EQUAL_EQUAL, GREATER, GREATER_EQUAL, LESS, LESS_EQUAL,
 
     // Literals.
     IDENTIFIER, STRING, NUMBER,
 
     // Keywords.
-    AND, CLASS, ELSE, FALSE, FUN, FOR, IF, NIL, OR, PRINT, RETURN, SUPER, THIS,
-    TRUE, VAR, WHILE,
+    AND, CLASS, ELSE, FALSE, FUN, FOR, IF, NIL, OR, PRINT, RETURN, SUPER, THIS, TRUE, VAR, WHILE, BREAK,
 
     EOF
 }

src/com/craftinginterpreters/tool/GenerateAst.java

@@ -22,7 +22,7 @@ public class GenerateAst {
         defineAst(outputDir, "Stmt",
                 Arrays.asList("Block : List<Stmt> statements", "Expression : Expr expression",
                         "If : Expr condition, Stmt thenBranch, Stmt elseBranch", "Print : Expr expression",
-                        "Var : Token name, Expr initializer", "While : Expr condition, Stmt body"));
+                        "Var : Token name, Expr initializer", "While : Expr condition, Stmt body", "Break : "));
     }
 
     private static void defineAst(String outputDir, String baseName, List<String> types) throws IOException {
@@ -71,9 +71,11 @@ public class GenerateAst {
         // Store parameters in fields.
         String[] fields = fieldList.split(", ");
         for (String field : fields) {
+            if (!field.isEmpty()) {
                 String name = field.split(" ")[1];
                 writer.println("      this." + name + " = " + name + ";");
             }
+        }
 
         writer.println("    }");
 
@@ -87,8 +89,10 @@ public class GenerateAst {
         // Fields
         writer.println();
         for (String field : fields) {
+            if (!field.isEmpty()) {
                 writer.println("    final " + field + ";");
             }
+        }
 
         writer.println("  }");
     }