Add ExprStatement PrintStatement

jlox/lox/src/main/java/xyz/ctsk/lox/Interpreter.java

@@ -1,16 +1,21 @@
 package xyz.ctsk.lox;
 
-public class Interpreter implements Expr.Visitor<Object> {
+import java.util.List;
 
-    void interpret(Expr expression) {
+public class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
+
+    void interpret(List<Stmt> statements) {
         try {
-            Object value = evaluate(expression);
-            System.out.println(stringify(value));
+            statements.forEach(this::execute);
         } catch (RuntimeError error) {
             Lox.runtimeError(error);
         }
     }
 
+    private void execute(Stmt stmt) {
+        stmt.accept(this);
+    }
+
     private Object evaluate(Expr expr) {
         return expr.accept(this);
     }
@@ -26,6 +31,18 @@ public class Interpreter implements Expr.Visitor<Object> {
         return text;
     }
 
+    @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 binary) {

jlox/lox/src/main/java/xyz/ctsk/lox/Lox.java

@@ -6,6 +6,7 @@ import java.io.InputStreamReader;
 import java.nio.charset.Charset;
 import java.nio.file.Files;
 import java.nio.file.Paths;
+import java.util.List;
 
 public class Lox {
     private static final Interpreter interpreter = new Interpreter();
@@ -40,11 +41,11 @@ public class Lox {
         var tokens = scanner.scanTokens();
 
         Parser parser = new Parser(tokens);
-        Expr expression = parser.parse();
+        List<Stmt> statements = parser.parse();
 
         if (hadError) return;
 
-        interpreter.interpret(expression);
+        interpreter.interpret(statements);
     }
 
     private static void runPrompt() throws IOException {

jlox/lox/src/main/java/xyz/ctsk/lox/Parser.java

@@ -1,5 +1,6 @@
 package xyz.ctsk.lox;
 
+import java.util.ArrayList;
 import java.util.List;
 
 import static xyz.ctsk.lox.TokenType.*;
@@ -8,6 +9,11 @@ import static xyz.ctsk.lox.TokenType.*;
  *
  * A recursive descent parser for the following grammar:
  * <p>
+ * program        → statement* EOF ;
+ * statement      → exprStmt
+ *                | printStmt ;
+ * exprStmt       → expression ";" ;
+ * printStmt      → "print" expression ";" ;
  * expression     → equality ;
  * equality       → comparison ( ( "!=" | "==" ) comparison )* ;
  * comparison     → term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
@@ -27,12 +33,32 @@ public class Parser {
         this.tokens = tokens;
     }
 
-    Expr parse() {
-        try {
-            return expression();
-        } catch (ParseError error) {
-            return null;
+    List<Stmt> parse() {
+        List<Stmt> statements = new ArrayList<>();
+
+        while (!isAtEnd()) {
+            statements.add(statement());
         }
+
+        return statements;
+    }
+
+
+
+    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 expression() {

jlox/lox/src/main/java/xyz/ctsk/lox/package-info.java

@@ -5,6 +5,11 @@
                         @Rule(head = "Grouping", body = {"Expr expression"}),
                         @Rule(head = "Literal", body = {"Object value"}),
                         @Rule(head = "Unary", body = {"Token operator", "Expr right"})
+                }),
+        @Root(name = "Stmt",
+                rules = {
+                        @Rule(head = "Expression", body = "Expr expression"),
+                        @Rule(head = "Print", body = "Expr expression")
                 })
 })
 package xyz.ctsk.lox;