From a4c1076008e1e7be767d7a8cbf9e5287b73d6c92 Mon Sep 17 00:00:00 2001
From: ctsk <9384305+ctsk@users.noreply.github.com>
Date: Sat, 10 Sep 2022 11:21:25 +0200
Subject: [PATCH] [jlox] Add while statement

---
 .../src/main/java/xyz/ctsk/lox/Interpreter.java  |  8 ++++++++
 jlox/lox/src/main/java/xyz/ctsk/lox/Parser.java  | 16 +++++++++++++++-
 .../src/main/java/xyz/ctsk/lox/package-info.java |  3 ++-
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/jlox/lox/src/main/java/xyz/ctsk/lox/Interpreter.java b/jlox/lox/src/main/java/xyz/ctsk/lox/Interpreter.java
index b08512f..177acd8 100644
--- a/jlox/lox/src/main/java/xyz/ctsk/lox/Interpreter.java
+++ b/jlox/lox/src/main/java/xyz/ctsk/lox/Interpreter.java
@@ -79,6 +79,14 @@ public class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         return null;
     }
 
+    @Override
+    public Void visitWhileStmt(Stmt.While stmt) {
+        while (isTruthy(evaluate(stmt.condition()))) {
+            execute(stmt.body());
+        }
+        return null;
+    }
+
     @Override
     public Object visitAssignExpr(Expr.Assign expr) {
         var value = evaluate(expr.value());
diff --git a/jlox/lox/src/main/java/xyz/ctsk/lox/Parser.java b/jlox/lox/src/main/java/xyz/ctsk/lox/Parser.java
index d2e3323..7e40615 100644
--- a/jlox/lox/src/main/java/xyz/ctsk/lox/Parser.java
+++ b/jlox/lox/src/main/java/xyz/ctsk/lox/Parser.java
@@ -17,10 +17,13 @@ import static xyz.ctsk.lox.TokenType.*;
  * statement      → exprStmt
  *                | ifStmt
  *                | printStmt
+ *                | whileStmt
  *                | block ;
  * block          → "{" declaration* "}" ;
- * exprStmt       → expression ";" ;
+ * ifStmt         → "if" "(" expression ")" statement ( "else" statement )? ;
+ * whileStmt      → "while" "(" expression ")" statement ;
  * printStmt      → "print" expression ";" ;
+ * exprStmt       → expression ";" ;
  * expression     → equality ;
  * expression     → assignment ;
  * assignment     → IDENTIFIER "=" assignment
@@ -81,10 +84,12 @@ public class Parser {
     private Stmt statement() {
         if (match(IF)) return ifStatement();
         if (match(PRINT)) return printStatement();
+        if (match(WHILE)) return whileStatement();
         if (match(LEFT_BRACE)) return new Stmt.Block(blockStatement());
         return expressionStatement();
     }
 
+
     private Stmt ifStatement() {
         consume(LEFT_PAREN, "Expect '(' after 'if'.");
         Expr condition = expression();
@@ -102,6 +107,15 @@ public class Parser {
         return new Stmt.Print(value);
     }
 
+    private Stmt whileStatement() {
+        consume(LEFT_PAREN, "Expect '(' after 'while'.");
+        Expr condition = expression();
+        consume(RIGHT_PAREN, "Expect ')' after condition.");
+
+        Stmt body = statement();
+
+        return new Stmt.While(condition, body);
+    }
     private List<Stmt> blockStatement() {
         var statements = new ArrayList<Stmt>();
 
diff --git a/jlox/lox/src/main/java/xyz/ctsk/lox/package-info.java b/jlox/lox/src/main/java/xyz/ctsk/lox/package-info.java
index 153f3be..7f75faf 100644
--- a/jlox/lox/src/main/java/xyz/ctsk/lox/package-info.java
+++ b/jlox/lox/src/main/java/xyz/ctsk/lox/package-info.java
@@ -15,7 +15,8 @@
                         @Rule(head = "Expression", body = {"Expr expression"}),
                         @Rule(head = "If", body = {"Expr condition", "Stmt thenBranch", "Stmt elseBranch"}),
                         @Rule(head = "Print", body = {"Expr expression"}),
-                        @Rule(head = "Var", body = {"Token name", "Expr initializer"})
+                        @Rule(head = "Var", body = {"Token name", "Expr initializer"}),
+                        @Rule(head = "While", body = {"Expr condition", "Stmt body"})
                 })
 })
 package xyz.ctsk.lox;