Chapter 8: Add expression and print statements

src/com/craftinginterpreters/lox/Interpreter.java

@@ -1,6 +1,8 @@
 package com.craftinginterpreters.lox;
 
-class Interpreter implements Expr.Visitor<Object> {
+import java.util.List;
+
+class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
     @Override
     public Object visitLiteralExpr(Expr.Literal expr) {
         return expr.value;
@@ -76,6 +78,23 @@ class Interpreter implements Expr.Visitor<Object> {
         return expr.accept(this);
     }
 
+    private void execute(Stmt stmt) {
+        stmt.accept(this);
+    }
+
+    @Override
+    public Void visitExpressionStmt(Stmt.Expression stmt) {
+        evaluate(stmt.expression);
+        return null;
+    }
+
+    @Override
+    public Void visitPrintStmt(Stmt.Print stmt) {
+        Object value = evaluate(stmt.expression);
+        System.out.println(stringify(value));
+        return null;
+    }
+
     @Override
     public Object visitBinaryExpr(Expr.Binary expr) {
         Object left = evaluate(expr.left);
@@ -123,10 +142,11 @@ class Interpreter implements Expr.Visitor<Object> {
         return null;
     }
 
-    public void interpret(Expr expression) {
+    public void interpret(List<Stmt> statements) {
         try {
-            Object value = evaluate(expression);
+            for (Stmt statement : statements) {
-            System.out.println(stringify(value));
+                execute(statement);
+            }
         } catch (RuntimeError error) {
             Lox.runtimeError(error);
         }

src/com/craftinginterpreters/lox/Lox.java

@@ -53,13 +53,13 @@ public class Lox {
         Scanner scanner = new Scanner(source);
         List<Token> tokens = scanner.scanTokens();
         Parser parser = new Parser(tokens);
-        Expr expression = parser.parse();
+        List<Stmt> statements = parser.parse();
 
         // Stop if there was a syntax error
         if (hadError)
             return;
 
-        interpreter.interpret(expression);
+        interpreter.interpret(statements);
     }
 
     public static void error(int line, String message) {

src/com/craftinginterpreters/lox/Parser.java

@@ -2,6 +2,7 @@ package com.craftinginterpreters.lox;
 
 import static com.craftinginterpreters.lox.TokenType.*;
 
+import java.util.ArrayList;
 import java.util.List;
 
 class Parser {
@@ -15,18 +16,39 @@ class Parser {
         this.tokens = tokens;
     }
 
-    public Expr parse() {
+    public List<Stmt> parse() {
-        try {
+        List<Stmt> statements = new ArrayList<>();
-            return expression();
+
-        } catch (ParseError error) {
+        while (!isAtEnd()) {
-            return null;
+            statements.add(statement());
         }
+
+        return statements;
     }
 
     private Expr expression() {
         return equality();
     }
 
+    private Stmt statement() {
+        if (match(PRINT))
+            return printStatement();
+
+        return expressionStatement();
+    }
+
+    private Stmt printStatement() {
+        Expr value = expression();
+        consume(SEMICOLON, "Expect ';' after value.");
+        return new Stmt.Print(value);
+    }
+
+    private Stmt expressionStatement() {
+        Expr expr = expression();
+        consume(SEMICOLON, "Expect ';' after expression.");
+        return new Stmt.Expression(expr);
+    }
+
     private Expr equality() {
         Expr expr = comparison();